diff --git a/documentation/RELEASE_NOTES.html b/documentation/RELEASE_NOTES.html
index 84e8899e9..93345e652 100644
--- a/documentation/RELEASE_NOTES.html
+++ b/documentation/RELEASE_NOTES.html
@@ -16,6 +16,11 @@
 
 <!-- Insert new items immediately below here ... -->
 
+<h3>Unsetting environment variables</h3>
+
+<p>The new command <code>epicsEnvUnset <i>varname</i></code> can be used to
+unset an environment variable.</p>
+
 <h3>Warning indicators in msi (and macLib) output</h3>
 
 <p>The libCom macro expansion library has been modified so that when the
diff --git a/src/libCom/env/envDefs.h b/src/libCom/env/envDefs.h
index ac6132541..20f0eb2ad 100644
--- a/src/libCom/env/envDefs.h
+++ b/src/libCom/env/envDefs.h
@@ -95,6 +95,7 @@ epicsShareFunc long epicsShareAPI
     envGetBoolConfigParam(const ENV_PARAM *pParam, int *pBool);
 epicsShareFunc long epicsShareAPI epicsPrtEnvParams(void);
 epicsShareFunc void epicsShareAPI epicsEnvSet (const char *name, const char *value);
+epicsShareFunc void epicsShareAPI epicsEnvUnset (const char *name);
 epicsShareFunc void epicsShareAPI epicsEnvShow (const char *name);
 
 #ifdef __cplusplus
diff --git a/src/libCom/iocsh/libComRegister.c b/src/libCom/iocsh/libComRegister.c
index d3a5cfac4..d8429fa9f 100644
--- a/src/libCom/iocsh/libComRegister.c
+++ b/src/libCom/iocsh/libComRegister.c
@@ -110,6 +110,21 @@ static void epicsEnvSetCallFunc(const iocshArgBuf *args)
     epicsEnvSet (name, value);
 }
 
+/* epicsEnvUnset */
+static const iocshArg epicsEnvUnsetArg0 = { "name",iocshArgString};
+static const iocshArg * const epicsEnvUnsetArgs[1] = {&epicsEnvUnsetArg0};
+static const iocshFuncDef epicsEnvUnsetFuncDef = {"epicsEnvUnset",1,epicsEnvUnsetArgs};
+static void epicsEnvUnsetCallFunc(const iocshArgBuf *args)
+{
+    char *name = args[0].sval;
+
+    if (name == NULL) {
+        fprintf(stderr, "Missing environment variable name argument.\n");
+        return;
+    }
+    epicsEnvUnset (name);
+}
+
 /* epicsParamShow */
 static const iocshFuncDef epicsParamShowFuncDef = {"epicsParamShow",0,NULL};
 static void epicsParamShowCallFunc(const iocshArgBuf *args)
@@ -367,6 +382,7 @@ void epicsShareAPI libComRegister(void)
     iocshRegister(&pwdFuncDef, pwdCallFunc);
 
     iocshRegister(&epicsEnvSetFuncDef, epicsEnvSetCallFunc);
+    iocshRegister(&epicsEnvUnsetFuncDef, epicsEnvUnsetCallFunc);
     iocshRegister(&epicsParamShowFuncDef, epicsParamShowCallFunc);
     iocshRegister(&epicsPrtEnvParamsFuncDef, epicsPrtEnvParamsCallFunc);
     iocshRegister(&epicsEnvShowFuncDef, epicsEnvShowCallFunc);
diff --git a/src/libCom/osi/os/Darwin/osdEnv.c b/src/libCom/osi/os/Darwin/osdEnv.c
index ab3f93644..f7ff12ced 100644
--- a/src/libCom/osi/os/Darwin/osdEnv.c
+++ b/src/libCom/osi/os/Darwin/osdEnv.c
@@ -39,6 +39,16 @@ epicsShareFunc void epicsShareAPI epicsEnvSet (const char *name, const char *val
     setenv(name, value, 1);
 }
 
+/*
+ * Unset an environment variable
+ */
+
+epicsShareFunc void epicsShareAPI epicsEnvUnset (const char *name)
+{
+    iocshEnvClear(name);
+    unsetenv(name);
+}
+
 /*
  * Show the value of the specified, or all, environment variables
  */
diff --git a/src/libCom/osi/os/default/osdEnv.c b/src/libCom/osi/os/default/osdEnv.c
index 682bcc934..0f6fb250d 100644
--- a/src/libCom/osi/os/default/osdEnv.c
+++ b/src/libCom/osi/os/default/osdEnv.c
@@ -55,6 +55,18 @@ epicsShareFunc void epicsShareAPI epicsEnvSet (const char *name, const char *val
 	}
 }
 
+/*
+ * Unset an environment variable
+ * Using putenv with a an existing name but without "=..." deletes
+ */
+
+epicsShareFunc void epicsShareAPI epicsEnvUnset (const char *name)
+{
+    iocshEnvClear(name);
+    if (getenv(name) != NULL)
+        putenv((char*)name);
+}
+
 /*
  * Show the value of the specified, or all, environment variables
  */
diff --git a/src/libCom/osi/os/iOS/osdEnv.c b/src/libCom/osi/os/iOS/osdEnv.c
index a32cce5ef..0c256725c 100644
--- a/src/libCom/osi/os/iOS/osdEnv.c
+++ b/src/libCom/osi/os/iOS/osdEnv.c
@@ -36,6 +36,16 @@ epicsShareFunc void epicsShareAPI epicsEnvSet (const char *name, const char *val
     setenv(name, value, 1);
 }
 
+/*
+ * Unset an environment variable
+ */
+
+epicsShareFunc void epicsShareAPI epicsEnvUnset (const char *name)
+{
+    iocshEnvClear(name);
+    unsetenv(name);
+}
+
 /*
  * Show the value of the specified, or all, environment variables
  */
diff --git a/src/libCom/osi/os/vxWorks/osdEnv.c b/src/libCom/osi/os/vxWorks/osdEnv.c
index c81f49316..88e0ba078 100644
--- a/src/libCom/osi/os/vxWorks/osdEnv.c
+++ b/src/libCom/osi/os/vxWorks/osdEnv.c
@@ -51,6 +51,25 @@ epicsShareFunc void epicsShareAPI epicsEnvSet (const char *name, const char *val
     }
 }
 
+/*
+ * Unset an environment variable
+ * Basically destroy the name of that variable because vxWorks does not
+ * support to really unset an environment variable.
+ */
+
+epicsShareFunc void epicsShareAPI epicsEnvUnset (const char *name)
+{
+    char* var;
+
+    if (!name) return;
+    iocshEnvClear(name);
+    var = getenv(name);
+    if (!var) return;
+    var -= strlen(name);
+    var --;
+    *var = 0;
+}
+
 /*
  * Show the value of the specified, or all, environment variables
  */
diff --git a/src/libCom/test/Makefile b/src/libCom/test/Makefile
index 89eb87f6f..c80339317 100755
--- a/src/libCom/test/Makefile
+++ b/src/libCom/test/Makefile
@@ -62,6 +62,11 @@ epicsEnvTest_SRCS += epicsEnvTest.c
 testHarness_SRCS += epicsEnvTest.c
 TESTS += epicsEnvTest
 
+TESTPROD_HOST += epicsEnvUnsetTest
+epicsEnvUnsetTest_SRCS += epicsEnvUnsetTest.c
+testHarness_SRCS += epicsEnvUnsetTest.c
+TESTS += epicsEnvUnsetTest
+
 TESTPROD_HOST += epicsErrlogTest
 epicsErrlogTest_SRCS += epicsErrlogTest.c
 testHarness_SRCS += epicsErrlogTest.c
diff --git a/src/libCom/test/epicsEnvUnsetTest.c b/src/libCom/test/epicsEnvUnsetTest.c
new file mode 100644
index 000000000..e9d0f8603
--- /dev/null
+++ b/src/libCom/test/epicsEnvUnsetTest.c
@@ -0,0 +1,37 @@
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+
+#include "macLib.h"
+#include "envDefs.h"
+#include "errlog.h"
+#include "epicsUnitTest.h"
+#include "testMain.h"
+
+static void check(const char* variable, const char* expected)
+{
+    const char* value;
+
+    value = getenv(variable);
+    if (!testOk((!expected && !value) || (expected && value && strcmp(expected, value) == 0),
+        "%s = \"%s\"", variable, value))
+    {
+        testDiag("should have been \"%s\"", expected);
+    }
+}
+
+MAIN(epicsEnvUnsetTest)
+{
+    eltc(0);
+    testPlan(3);
+
+    check("TEST_VAR_A",NULL);
+    epicsEnvSet("TEST_VAR_A","test value");
+    check("TEST_VAR_A","test value");
+    epicsEnvUnset("TEST_VAR_A");
+    check("TEST_VAR_A",NULL);
+
+    testDone();
+    return 0;
+}