diff --git a/all.sas b/all.sas
index 0600468..2c58470 100644
--- a/all.sas
+++ b/all.sas
@@ -2413,10 +2413,29 @@ run;
 
         %mp_binarycopy(inloc="/home/me/blah.txt", outref=_webout)
 
-  @param inloc full, quoted "path/and/filename.ext" of the object to be copied
-  @param outloc full, quoted "path/and/filename.ext" of object to be created
-  @param inref can override default input fileref to avoid naming clash
-  @param outref an override default output fileref to avoid naming clash
+  To append to a file, use the mode option, eg:
+
+      filename tmp1 temp;
+      filename tmp2 temp;
+      data _null_;
+        file tmp1;
+        put 'stacking';
+      run;
+
+      %mp_binarycopy(inref=tmp1, outref=tmp2, mode=APPEND)
+      %mp_binarycopy(inref=tmp1, outref=tmp2, mode=APPEND)
+
+
+  @param [in] inloc quoted "path/and/filename.ext" of the file to be copied
+  @param [out] outloc quoted "path/and/filename.ext" of the file to be created
+  @param [in] inref (____in) If provided, this fileref will take precedence over
+    the `inloc` parameter
+  @param [out] outref (____in) If provided, this fileref will take precedence
+    over the `outloc` parameter.  It must already exist!
+  @param [in] mode (CREATE) Valid values:
+    @li CREATE - Create the file (even if it already exists)
+    @li APPEND - Append to the file (don't overwrite)
+
   @returns nothing
 
   @version 9.2
@@ -2428,20 +2447,29 @@ run;
     ,outloc=          /* full path and filename of object to be created */
     ,inref=____in   /* override default to use own filerefs */
     ,outref=____out /* override default to use own filerefs */
+    ,mode=CREATE
 )/*/STORE SOURCE*/;
+  %local mod outmode;
+  %if &mode=APPEND %then %do;
+    %let mod=mod;
+    %let outmode='a';
+  %end;
+  %else %do;
+    %let outmode='o';
+  %end;
   /* these IN and OUT filerefs can point to anything */
   %if &inref = ____in %then %do;
     filename &inref &inloc lrecl=1048576 ;
   %end;
   %if &outref=____out %then %do;
-    filename &outref &outloc lrecl=1048576 ;
+    filename &outref &outloc lrecl=1048576 &mod;
   %end;
 
   /* copy the file byte-for-byte  */
   data _null_;
     length filein 8 fileid 8;
     filein = fopen("&inref",'I',1,'B');
-    fileid = fopen("&outref",'O',1,'B');
+    fileid = fopen("&outref",&outmode,1,'B');
     rec = '20'x;
     do while(fread(filein)=0);
       rc = fget(filein,rec,1);
diff --git a/base/mp_binarycopy.sas b/base/mp_binarycopy.sas
index d964a73..abc7e91 100755
--- a/base/mp_binarycopy.sas
+++ b/base/mp_binarycopy.sas
@@ -9,10 +9,29 @@
 
         %mp_binarycopy(inloc="/home/me/blah.txt", outref=_webout)
 
-  @param inloc full, quoted "path/and/filename.ext" of the object to be copied
-  @param outloc full, quoted "path/and/filename.ext" of object to be created
-  @param inref can override default input fileref to avoid naming clash
-  @param outref an override default output fileref to avoid naming clash
+  To append to a file, use the mode option, eg:
+
+      filename tmp1 temp;
+      filename tmp2 temp;
+      data _null_;
+        file tmp1;
+        put 'stacking';
+      run;
+
+      %mp_binarycopy(inref=tmp1, outref=tmp2, mode=APPEND)
+      %mp_binarycopy(inref=tmp1, outref=tmp2, mode=APPEND)
+
+
+  @param [in] inloc quoted "path/and/filename.ext" of the file to be copied
+  @param [out] outloc quoted "path/and/filename.ext" of the file to be created
+  @param [in] inref (____in) If provided, this fileref will take precedence over
+    the `inloc` parameter
+  @param [out] outref (____in) If provided, this fileref will take precedence
+    over the `outloc` parameter.  It must already exist!
+  @param [in] mode (CREATE) Valid values:
+    @li CREATE - Create the file (even if it already exists)
+    @li APPEND - Append to the file (don't overwrite)
+
   @returns nothing
 
   @version 9.2
@@ -24,20 +43,29 @@
     ,outloc=          /* full path and filename of object to be created */
     ,inref=____in   /* override default to use own filerefs */
     ,outref=____out /* override default to use own filerefs */
+    ,mode=CREATE
 )/*/STORE SOURCE*/;
+  %local mod outmode;
+  %if &mode=APPEND %then %do;
+    %let mod=mod;
+    %let outmode='a';
+  %end;
+  %else %do;
+    %let outmode='o';
+  %end;
   /* these IN and OUT filerefs can point to anything */
   %if &inref = ____in %then %do;
     filename &inref &inloc lrecl=1048576 ;
   %end;
   %if &outref=____out %then %do;
-    filename &outref &outloc lrecl=1048576 ;
+    filename &outref &outloc lrecl=1048576 &mod;
   %end;
 
   /* copy the file byte-for-byte  */
   data _null_;
     length filein 8 fileid 8;
     filein = fopen("&inref",'I',1,'B');
-    fileid = fopen("&outref",'O',1,'B');
+    fileid = fopen("&outref",&outmode,1,'B');
     rec = '20'x;
     do while(fread(filein)=0);
       rc = fget(filein,rec,1);
diff --git a/tests/crossplatform/mp_binarycopy.test.sas b/tests/crossplatform/mp_binarycopy.test.sas
new file mode 100644
index 0000000..b456c21
--- /dev/null
+++ b/tests/crossplatform/mp_binarycopy.test.sas
@@ -0,0 +1,99 @@
+/**
+  @file
+  @brief Testing mp_binarycopy.sas macro
+
+  <h4> SAS Macros </h4>
+  @li mp_binarycopy.sas
+  @li mp_assert.sas
+
+**/
+
+
+/* TEST 1 - regular file copy */
+%let string1=test1;
+filename tmp temp;
+filename myref temp;
+data _null_;
+  file tmp;
+  put "&string1";
+run;
+%mp_binarycopy(inref=tmp, outref=myref)
+data _null_;
+  infile myref;
+  input;
+  put _infile_;
+  call symputx('string1_check',_infile_);
+  stop;
+run;
+%mp_assert(
+  iftrue=("&string1"="&string1_check"),
+  desc=Basic String Compare,
+  outds=work.test_results
+)
+
+
+/* TEST 2 - File append */
+%let string2=test2;
+%let path2=%sysfunc(pathname(work))/somefile.txt;
+data _null_;
+  file "&path2";
+  put "&string2";
+run;
+%mp_binarycopy(inloc="&path2", outref=myref, mode=APPEND)
+data _null_;
+  infile myref;
+  input;
+  put _infile_;
+  if _n_=2 then call symputx('string2_check',_infile_);
+run;
+%mp_assert(
+  iftrue=("&string2"="&string2_check"),
+  desc=Append Check (file to ref),
+  outds=work.test_results
+)
+
+/* TEST 3 - File create (ref to existing file) */
+%let string3=test3;
+%let path3=%sysfunc(pathname(work))/somefile3.txt;
+filename tmp3 temp;
+data _null_;
+  file tmp3;
+  put "&string3";
+run;
+data _null_;
+  file "&path3";
+  put "this should not be returned";
+run;
+%mp_binarycopy(inref=tmp3, outloc="&path3")
+data _null_;
+  infile "&path3";
+  input;
+  put _infile_;
+  if _n_=1 then call symputx('string3_check',_infile_);
+run;
+%mp_assert(
+  iftrue=("&string3"="&string3_check"),
+  desc=Append Check (ref to existing file),
+  outds=work.test_results
+)
+
+/* TEST 4 - File append (ref to file) */
+%let string4=test4;
+%let string4_check=;
+filename tmp4 temp;
+data _null_;
+  file tmp4;
+  put "&string4";
+run;
+%mp_binarycopy(inref=tmp4, outloc="&path3",mode=APPEND)
+data _null_;
+  infile "&path3";
+  input;
+  put _infile_;
+  if _n_=2 then call symputx('string4_check',_infile_);
+run;
+%mp_assert(
+  iftrue=("&string4"="&string4_check"),
+  desc=Append Check (ref to file),
+  outds=work.test_results
+)
\ No newline at end of file