diff --git a/ProcessLib/ProcessOutput.cpp b/ProcessLib/ProcessOutput.cpp
index fd130468a9417eae8d8b8239f0c91d51de1f52ea..a49ded0a4802164ebe1bbdd7df6e2c9e8cfd6f22 100644
--- a/ProcessLib/ProcessOutput.cpp
+++ b/ProcessLib/ProcessOutput.cpp
@@ -15,10 +15,7 @@
 namespace ProcessLib
 {
 
-ProcessOutput::ProcessOutput(BaseLib::ConfigTree const& output_config,
-              std::vector<std::reference_wrapper<ProcessVariable>> const&
-              process_variables,
-              SecondaryVariableCollection const& secondary_variables)
+ProcessOutput::ProcessOutput(BaseLib::ConfigTree const& output_config)
 {
     //! \ogs_file_param{process__output__variables}
     auto const out_vars = output_config.getConfigSubtree("variables");
diff --git a/ProcessLib/ProcessOutput.h b/ProcessLib/ProcessOutput.h
index d791b0ac17c5f561ceceb0d1b80da9e2835ac8cf..db13504f76676e20efd38b0c4abb6655586bd8fe 100644
--- a/ProcessLib/ProcessOutput.h
+++ b/ProcessLib/ProcessOutput.h
@@ -20,10 +20,7 @@ namespace ProcessLib
 struct ProcessOutput final
 {
     //! Constructs a new instance.
-    ProcessOutput(BaseLib::ConfigTree const& output_config,
-                  std::vector<std::reference_wrapper<ProcessVariable>> const&
-                  process_variables,
-                  SecondaryVariableCollection const& secondary_variables);
+    ProcessOutput(BaseLib::ConfigTree const& output_config);
 
     //! All variables that shall be output.
     std::set<std::string> output_variables;
diff --git a/ProcessLib/SecondaryVariable.cpp b/ProcessLib/SecondaryVariable.cpp
index ee7f24b3cca1852b226b7ca4fe514e6dee2e67e2..170329384eecbe37e520fb585240ec4f1cb53cf5 100644
--- a/ProcessLib/SecondaryVariable.cpp
+++ b/ProcessLib/SecondaryVariable.cpp
@@ -12,17 +12,6 @@
 namespace ProcessLib
 {
 
-SecondaryVariableCollection::SecondaryVariableCollection(
-        std::initializer_list<std::string> internal_names)
-{
-    // read which variables are defined in the config
-    for (auto const& internal_name : internal_names) {
-        if (!_all_secondary_variables.insert(internal_name).second) {
-            OGS_FATAL("Tag name <%s> has been specified twice as a secondary variable.");
-        }
-    }
-}
-
 void SecondaryVariableCollection::addNameMapping(std::string const& internal_name,
                                                  std::string const& external_name)
 {
@@ -35,13 +24,6 @@ void SecondaryVariableCollection::addNameMapping(std::string const& internal_nam
         "Secondary variable names must be unique.");
 }
 
-bool SecondaryVariableCollection::variableExists(
-    std::string const& external_name) const
-{
-    return _map_external_to_internal.find(external_name) !=
-           _map_external_to_internal.cend();
-}
-
 void SecondaryVariableCollection::addSecondaryVariable(
     std::string const& internal_name,
     const unsigned num_components,
diff --git a/ProcessLib/SecondaryVariable.h b/ProcessLib/SecondaryVariable.h
index dff5f9c006d3325215f0fe461aaf93557bf38355..065f56f806513f70e78305f2a06348ca02719a65 100644
--- a/ProcessLib/SecondaryVariable.h
+++ b/ProcessLib/SecondaryVariable.h
@@ -99,23 +99,10 @@ struct SecondaryVariable final
 class SecondaryVariableCollection final
 {
 public:
-    /*! Constructs new instance.
-     *
-     * \param internal_names list of internal variable names known initially.
-     */
-    SecondaryVariableCollection(
-            std::initializer_list<std::string> internal_names);
-
     //! Register a variable with the given internal and external names.
     void addNameMapping(std::string const& internal_name,
                         std::string const& external_name);
 
-    /*! Tells if a secondary variable with the specified name has been set up.
-     *
-     * \note \c external_name is not the tag name in the project file!
-     */
-    bool variableExists(std::string const& external_name) const;
-
     /*! Set up a secondary variable.
      *
      * \param internal_name the tag in the project file associated with this
@@ -132,20 +119,7 @@ public:
                               const unsigned num_components,
                               SecondaryVariableFunctions&& fcts);
 
-    //! Returns an iterator to the first secondary variable.
-    std::map<std::string, SecondaryVariable>::const_iterator
-    begin() const
-    {
-        return _configured_secondary_variables.begin();
-    }
-
-    //! Returns an iterator past the last secondary variable.
-    std::map<std::string, SecondaryVariable>::const_iterator
-    end() const
-    {
-        return _configured_secondary_variables.end();
-    }
-
+    //! Returns the secondary variable with the given external name.
     SecondaryVariable const& get(std::string const& external_name);
 
 private: