diff --git a/ChangeLog b/ChangeLog
index 4bbe7137..7c19f899 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,6 +4,7 @@
 
 changes since 0.17.0
 ===================================
+NEW 2016-04-22 Added the theory function muMinusExpTF for mu minus fits
 NEW 2016-02-23 It is now possible to export the averaged data/Fourier
 
 changes since 0.16.0
diff --git a/src/classes/PTheory.cpp b/src/classes/PTheory.cpp
index 30c0003c..3c093b3a 100644
--- a/src/classes/PTheory.cpp
+++ b/src/classes/PTheory.cpp
@@ -507,6 +507,10 @@ Double_t PTheory::Func(register Double_t t, const PDoubleVector& paramValues, co
           return Polynom(t, paramValues, funcValues) * fMul->Func(t, paramValues, funcValues) +
                  fAdd->Func(t, paramValues, funcValues);
           break;
+        case THEORY_MU_MINUS_EXP:
+          return MuMinusExpTF(t, paramValues, funcValues) * fMul->Func(t, paramValues, funcValues) +
+                 fAdd->Func(t, paramValues, funcValues);
+          break;
         case THEORY_USER_FCN:
           return UserFcn(t, paramValues, funcValues) * fMul->Func(t, paramValues, funcValues) +
                  fAdd->Func(t, paramValues, funcValues);
@@ -599,6 +603,9 @@ Double_t PTheory::Func(register Double_t t, const PDoubleVector& paramValues, co
         case THEORY_DYNAMIC_TF_NK:
           return DynamicNKTF (t, paramValues, funcValues) * fMul->Func(t, paramValues, funcValues);
           break;
+        case THEORY_MU_MINUS_EXP:
+          return MuMinusExpTF(t, paramValues, funcValues) * fMul->Func(t, paramValues, funcValues);
+          break;
         case THEORY_POLYNOM:
           return Polynom(t, paramValues, funcValues) * fMul->Func(t, paramValues, funcValues);
           break;
@@ -695,6 +702,9 @@ Double_t PTheory::Func(register Double_t t, const PDoubleVector& paramValues, co
         case THEORY_DYNAMIC_TF_NK:
           return DynamicNKTF (t, paramValues, funcValues) + fAdd->Func(t, paramValues, funcValues);
           break;
+        case THEORY_MU_MINUS_EXP:
+          return MuMinusExpTF(t, paramValues, funcValues) + fAdd->Func(t, paramValues, funcValues);
+          break;
         case THEORY_POLYNOM:
           return Polynom(t, paramValues, funcValues) + fAdd->Func(t, paramValues, funcValues);
           break;
@@ -789,6 +799,9 @@ Double_t PTheory::Func(register Double_t t, const PDoubleVector& paramValues, co
         case THEORY_DYNAMIC_TF_NK:
           return DynamicNKTF(t, paramValues, funcValues);
           break;
+        case THEORY_MU_MINUS_EXP:
+          return MuMinusExpTF(t, paramValues, funcValues);
+          break;
         case THEORY_POLYNOM:
           return Polynom(t, paramValues, funcValues);
           break;
@@ -2942,6 +2955,46 @@ Double_t PTheory::GetDynKTLFValue(const Double_t t) const
   return fDynLFFuncValue[idx]+df;
 }
 
+//--------------------------------------------------------------------------
+/**
+ * <p> theory function: MuMinusExpTF
+ *
+ * \f[ = N_0 \exp(-t/tau) [1 + A \exp(-\lambda t) \cos(2\pi\nu t + \phi)] \f]
+ *
+ * <b>meaning of paramValues:</b> \f$t_{\rm shift}\f$, \f$N_0\f$, \f$\tau\f$, \f$A\f$, \f$\lambda\f$, \f$\phi\f$, \f$\nu\f$
+ *
+ * <b>return:</b> function value
+ *
+ * \param t time in \f$(\mu\mathrm{s})\f$, or x-axis value for non-muSR fit
+ * \param paramValues parameter values
+ * \param funcValues vector with the functions (i.e. functions of the parameters)
+ */
+Double_t PTheory::MuMinusExpTF(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const
+{
+  // expected parameters: N0 tau A lambda phase frequency [tshift]
+
+  Double_t val[7];
+
+  assert(fParamNo.size() <= 7);
+
+  // check if FUNCTIONS are used
+  for (UInt_t i=0; i<fParamNo.size(); i++) {
+    if (fParamNo[i] < MSR_PARAM_FUN_OFFSET) { // parameter or resolved map
+      val[i] = paramValues[fParamNo[i]];
+    } else { // function
+      val[i] = funcValues[fParamNo[i]-MSR_PARAM_FUN_OFFSET];
+    }
+  }
+
+  Double_t tt;
+  if (fParamNo.size() == 6) // no tshift
+    tt = t;
+  else // tshift present
+    tt = t-val[6];
+
+  return val[0]*exp(-tt/val[1])*(1.0+val[2]*exp(-val[3]*tt)*cos(TWO_PI*val[5]*tt+DEG_TO_RAD*val[4]));
+}
+
 //--------------------------------------------------------------------------
 // END
 //--------------------------------------------------------------------------
diff --git a/src/include/PTheory.h b/src/include/PTheory.h
index 85f79ddf..528d7f09 100644
--- a/src/include/PTheory.h
+++ b/src/include/PTheory.h
@@ -70,8 +70,9 @@
 #define THEORY_STATIC_TF_NK                 24
 #define THEORY_DYNAMIC_ZF_NK                25
 #define THEORY_DYNAMIC_TF_NK                26
-#define THEORY_POLYNOM                      27
-#define THEORY_USER_FCN                     28
+#define THEORY_MU_MINUS_EXP                 27
+#define THEORY_POLYNOM                      28
+#define THEORY_USER_FCN                     29
 
 // function parameter tags, i.e. how many parameters has a specific function
 // if there is a comment with a (tshift), the number of parameters is increased by one
@@ -102,9 +103,10 @@
 #define THEORY_PARAM_STATIC_TF_NK                 4 // phase, frequency, damping D0, R_b=DGbG/D0 (tshift)
 #define THEORY_PARAM_DYNAMIC_ZF_NK                3 // damping D0, R_b=DGbG/D0, nu_c (tshift)
 #define THEORY_PARAM_DYNAMIC_TF_NK                5 // phase, frequency, damping D0, R_b=DGbG/D0, nu_c (tshift)
+#define THEORY_PARAM_MU_MINUS_EXP                 6 // N0, tau, A, damping, phase, frequency (tshift)
 
 // number of available user functions
-#define THEORY_MAX 29
+#define THEORY_MAX 30
 
 // maximal number of parameters. Needed in the contents of LF
 #define THEORY_MAX_PARAM 10
@@ -217,6 +219,9 @@ static PTheoDataBase fgTheoDataBase[THEORY_MAX] = {
   {THEORY_DYNAMIC_TF_NK, THEORY_PARAM_DYNAMIC_TF_NK, false,
    "dynamicNKTF", "dnktf", "(phase frequency damping_D0 R_b nu_c)", "(phase frequency damping_D0 R_b nu_c tshift)"},
 
+  {THEORY_MU_MINUS_EXP, THEORY_PARAM_MU_MINUS_EXP, false,
+   "muMinusExpTF", "mmsetf", "(N0 tau A lambda phase nu)", "(N0 tau A lambda phase nu tshift)"},
+
   {THEORY_POLYNOM, 0, false,
    "polynom", "p", "(tshift p0 p1 ... pn)", "(tshift p0 p1 ... pn)"},
 
@@ -272,6 +277,7 @@ class PTheory
     virtual Double_t StaticNKTF(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const;
     virtual Double_t DynamicNKZF(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const;
     virtual Double_t DynamicNKTF(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const;
+    virtual Double_t MuMinusExpTF(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const;
     virtual Double_t Polynom(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const;
     virtual Double_t UserFcn(register Double_t t, const PDoubleVector& paramValues, const PDoubleVector& funcValues) const;