diff --git a/DESCRIPTION b/DESCRIPTION
index 6c09a95..446aa94 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -45,6 +45,7 @@ Collate:
     'cobrar.R'
     'deadEndMetabolites.R'
     'fba.R'
+    'findExchReact.R'
     'fixBMRatios.R'
     'fluxBMCoupling.R'
     'fluxdist_analysis.R'
diff --git a/NAMESPACE b/NAMESPACE
index 6985fb4..178b5a0 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -11,6 +11,7 @@ export(addRows)
 export(addSingleConstraint)
 export(addSubsystem)
 export(changeBounds)
+export(changeObjFunc)
 export(checkCompartmentId)
 export(checkGeneId)
 export(checkMetId)
@@ -23,6 +24,7 @@ export(countElements)
 export(deadEndMetabolites)
 export(elements)
 export(fba)
+export(findExchReact)
 export(fixBMRatios)
 export(fluxBMCoupling)
 export(fva)
diff --git a/R/findExchReact.R b/R/findExchReact.R
new file mode 100644
index 0000000..82be623
--- /dev/null
+++ b/R/findExchReact.R
@@ -0,0 +1,62 @@
+#' Find exchange reactions
+#'
+#' Finds all exchange reactions within a (community) model and report them in a
+#' data frame.
+#'
+#' @param model Model of class \link{ModelOrg} or \link{ModelComm}
+#'
+#' @returns If 'model' is of class \link{ModelOrg}, a data.frame is returned
+#' stating all exchange reaction IDs, their index in the reaction list, the
+#' respective metabolite id, name, and index in the metabolite list. If the
+#' model is of class \link{ModelComm}, the resulting data.frame contains the
+#' community exchange reactions and the organism-specific exchange reaction. The
+#' latter are exchange reactions, that connect extracellular metabolites of the
+#' organism metabolic network models with the shared extracellular space.
+#'
+#' @export
+setGeneric("findExchReact" ,valueClass = "data.frame", function(model) {
+  standardGeneric("findExchReact")
+})
+setMethod("findExchReact", signature(model = "ModelOrg"),
+          function(model) {
+            ex_id <- model@react_id[grep("^EX_",model@react_id)]
+            ex_pos <- react_pos(model, ex_id)
+
+            cpd_pos <- apply(model@S[,ex_pos],2,function(x) which(x!=0))
+            cpd_id <- model@met_id[cpd_pos]
+            cpd_name <- model@met_name[cpd_pos]
+
+            return(data.frame(react_id = ex_id,
+                              react_pos = ex_pos,
+                              met_id = cpd_id,
+                              met_name = cpd_name,
+                              met_pos = cpd_pos,
+                              lb = model@lowbnd[ex_pos],
+                              ub = model@uppbnd[ex_pos]))
+          })
+setMethod("findExchReact", signature(model = "ModelComm"),
+          function(model) {
+            ex_id <- model@react_id[grep("^EX_",model@react_id)]
+            ex_pos <- react_pos(model, ex_id)
+
+            mex_id <- model@react_id[grep("^M[0-9]+_EX_",model@react_id)]
+            mex_pos <- react_pos(model, mex_id)
+
+            cpd_posEX <- apply(model@S[,ex_pos],2,function(x) which(x!=0))
+            cpd_posMEX <- apply(model@S[grep("^M[0-9]+",model@met_id),mex_pos],2,function(x) which(x!=0))
+            cpd_pos <- c(cpd_posEX, cpd_posMEX)
+            cpd_id <- model@met_id[cpd_pos]
+            cpd_name <- model@met_name[cpd_pos]
+
+            return(data.frame(exchange_type = c(rep("Community",length(ex_id)),
+                                                rep("Organism",length(mex_id))),
+                              organism_id = c(rep(NA_character_,length(ex_id)),
+                                              sub("(^M[0-9]+)_.*$","\\1",mex_id)),
+                              react_id = c(ex_id, mex_id),
+                              react_pos = c(ex_pos, mex_pos),
+                              met_id = cpd_id,
+                              met_name = cpd_name,
+                              met_pos = cpd_pos,
+                              lb = model@lowbnd[c(ex_pos,mex_pos)],
+                              ub = model@uppbnd[c(ex_pos,mex_pos)]))
+          })
diff --git a/R/model_modifications.R b/R/model_modifications.R
index 23f94b1..47ed8d2 100644
--- a/R/model_modifications.R
+++ b/R/model_modifications.R
@@ -999,3 +999,36 @@ setObjDir <- function(model, dir) {
 
   return(model)
 }
+
+#' Change the objective function
+#'
+#' Changes the objective function of a model.
+#'
+#' @param model Model of class \link{ModelOrg}
+#' @param react Character vector containing the model's reactions IDs, that are
+#' part of the new objective function
+#' @param obj_coef Numeric vector with the objective coefficients of the
+#' reactions in the vector 'react'.
+#'
+#' @details
+#' Reactions not listed in 'react' are assigned an objective coefficient of
+#' zero.
+#'
+#' @returns An updated model of class \link{ModelOrg}
+#'
+#' @export
+changeObjFunc <- function(model, react, obj_coef = rep(1, length(react))) {
+  if(length(react) != length(obj_coef))
+    stop("The arguments 'react' and 'obj_coef' should be vectors of the same length.")
+
+  if(!all(checkReactId(model, react))) {
+    stop("Please check your reaction IDs/indices in argument 'react'.")
+  }
+
+  react.idx <- react_pos(model, react)
+
+  model@obj_coef <- rep(0, react_num(model))
+  model@obj_coef[react.idx] <- obj_coef
+
+  return(model)
+}
diff --git a/_pkgdown.yml b/_pkgdown.yml
index d1b337b..309ffa8 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -27,6 +27,7 @@ reference:
       - addReact
       - addSubsystem
       - changeBounds
+      - changeObjFunc
       - setObjDir
       - rmCompartment
       - rmConstraint
@@ -51,6 +52,7 @@ reference:
       - gene_pos
       - geneDel
       - deadEndMetabolites
+      - findExchReact
       - printConstraint
       - printReaction
       - react_num
diff --git a/man/changeObjFunc.Rd b/man/changeObjFunc.Rd
new file mode 100644
index 0000000..4818f16
--- /dev/null
+++ b/man/changeObjFunc.Rd
@@ -0,0 +1,27 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/model_modifications.R
+\name{changeObjFunc}
+\alias{changeObjFunc}
+\title{Change the objective function}
+\usage{
+changeObjFunc(model, react, obj_coef = rep(1, length(react)))
+}
+\arguments{
+\item{model}{Model of class \link{ModelOrg}}
+
+\item{react}{Character vector containing the model's reactions IDs, that are
+part of the new objective function}
+
+\item{obj_coef}{Numeric vector with the objective coefficients of the
+reactions in the vector 'react'.}
+}
+\value{
+An updated model of class \link{ModelOrg}
+}
+\description{
+Changes the objective function of a model.
+}
+\details{
+Reactions not listed in 'react' are assigned an objective coefficient of
+zero.
+}
diff --git a/man/findExchReact.Rd b/man/findExchReact.Rd
new file mode 100644
index 0000000..4a77991
--- /dev/null
+++ b/man/findExchReact.Rd
@@ -0,0 +1,24 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/findExchReact.R
+\name{findExchReact}
+\alias{findExchReact}
+\title{Find exchange reactions}
+\usage{
+findExchReact(model)
+}
+\arguments{
+\item{model}{Model of class \link{ModelOrg} or \link{ModelComm}}
+}
+\value{
+If 'model' is of class \link{ModelOrg}, a data.frame is returned
+stating all exchange reaction IDs, their index in the reaction list, the
+respective metabolite id, name, and index in the metabolite list. If the
+model is of class \link{ModelComm}, the resulting data.frame contains the
+community exchange reactions and the organism-specific exchange reaction. The
+latter are exchange reactions, that connect extracellular metabolites of the
+organism metabolic network models with the shared extracellular space.
+}
+\description{
+Finds all exchange reactions within a (community) model and report them in a
+data frame.
+}