diff --git a/debug.lsp b/debug.lsp
index 166d5f0..3e2f9f6 100644
--- a/debug.lsp
+++ b/debug.lsp
@@ -5,6 +5,15 @@
 (print (string-ltrim "     abc"))
 (print (string-trim "  abc   "))
 
+(defun string-upcase (str) 
+    (string-case str "upper"))
+
+(defun string-downcase (str) 
+    (string-case str "lower"))
+
+(print (string-upcase "abcABCD"))
+(print (string-downcase "abcABCD"))
+
 ;; (print (sprintf "%.2f" (list 1.25)))
 
 ;; (print (sprintf "%.2f" '(1.23456)))
diff --git a/ml.cpp b/ml.cpp
index 1af8db5..e42e051 100644
--- a/ml.cpp
+++ b/ml.cpp
@@ -1564,6 +1564,16 @@ namespace builtin {
 	    return MlValue(result);
     }
 
+	// converts string to upper or lower case
+    MlValue string_case(std::vector<MlValue> args, MlEnvironment &env) {
+	    eval_args(args, env);
+
+	    if (args.size() != 2)
+		    throw MlError(MlValue("string_case", string_case), env, args.size() > 2 ? TOO_MANY_ARGS : TOO_FEW_ARGS);
+
+	    return MlValue::string(string_lucase(args[0].as_string(), args[1].as_string()));
+	}
+
 	// trims characters " \n\r\t" from left or right or both ends of a string
     MlValue string_rltrim(std::vector<MlValue> args, MlEnvironment &env) {
 	    eval_args(args, env);
@@ -1571,8 +1581,7 @@ namespace builtin {
 	    if (args.size() != 3)
 		    throw MlError(MlValue("string_rltrim", string_rltrim), env, args.size() > 3 ? TOO_MANY_ARGS : TOO_FEW_ARGS);
 
-	    // TODO validate
-	    return MlValue::string(trim(args[0].as_string(), args[1].as_string(), args[2].as_string()));
+	    return MlValue::string(string_trim(args[0].as_string(), args[1].as_string(), args[2].as_string()));
     }
 
     MlValue string_pad(std::vector<MlValue> args, MlEnvironment &env) {
@@ -1857,6 +1866,7 @@ MlValue MlEnvironment::get(const std::string &name) const {
 	if (name == "string-split") return MlValue("string-split", builtin::string_split);
 	if (name == "string-pad") return MlValue("string-pad", builtin::string_pad);
 	if (name == "string-rltrim") return MlValue("string-rltrim", builtin::string_rltrim);
+	if (name == "string-case") return MlValue("string-case", builtin::string_case);
 
 	// Casting operations
 	if (name == "int") return MlValue("int", builtin::cast_to_int);
diff --git a/ml_string.cpp b/ml_string.cpp
index ca0425d..ac7e9d6 100644
--- a/ml_string.cpp
+++ b/ml_string.cpp
@@ -43,7 +43,17 @@ std::vector<std::string> regexp_strsplit(const std::string &string_to_split, con
 	return elems;
 }
 
-std::string trim(std::string s, const std::string &chars_to_trim, const std::string &rltrim) {
+std::string string_lucase(std::string s, const std::string &strcase) {
+	if (strcase == "upper")
+		std::transform(s.begin(), s.end(),s.begin(), ::toupper);
+	
+	if (strcase == "lower")
+		std::transform(s.begin(), s.end(),s.begin(), ::tolower);
+	
+	return s;
+}
+
+std::string string_trim(std::string s, const std::string &chars_to_trim, const std::string &rltrim) {
 	if (rltrim == "ltrim" || rltrim == "trim")
 		s.erase(0, s.find_first_not_of(chars_to_trim));
 	
diff --git a/ml_string.h b/ml_string.h
index 00c68ab..7710a7b 100644
--- a/ml_string.h
+++ b/ml_string.h
@@ -14,6 +14,8 @@ bool regexp_search(const std::string &where, const std::string &regex_str);
 
 std::vector<std::string> regexp_strsplit(const std::string &string_to_split, const std::string &rgx_str);
 
-std::string trim(std::string s, const std::string &chars_to_trim, const std::string &rltrim);
+std::string string_lucase(std::string s, const std::string &strcase);
+
+std::string string_trim(std::string s, const std::string &chars_to_trim, const std::string &rltrim);
 
 std::string string_padd(const std::string & str, int pad_len, char fill_char, bool from_right);
\ No newline at end of file
diff --git a/stdlib/stdlib.lsp b/stdlib/stdlib.lsp
index eeb8069..617304e 100644
--- a/stdlib/stdlib.lsp
+++ b/stdlib/stdlib.lsp
@@ -24,16 +24,17 @@
 (defun string-trim (str) 
     (string-rltrim str " \n\r\t" "trim"))
 
-; pad string on the end
 (defun string-rpad (str length pad_char)
     (string-pad str length pad_char "rpad"))
-
-; pad string on the begining
 (defun string-lpad (str length pad_char)
     (string-pad str length pad_char "lpad"))
 
+(defun string-upcase (str) 
+    (string-case str "upper"))
+(defun string-downcase (str) 
+    (string-case str "lower"))
 
-; pause for interval
+; pause for interval of seconds
 (defun sleep (time) 
   (system-cmd (+ "sleep " (string time))))
 
diff --git a/tests/test.lsp b/tests/test.lsp
index 19837f0..d261f2c 100644
--- a/tests/test.lsp
+++ b/tests/test.lsp
@@ -186,4 +186,9 @@
 (print (get-env "HOME"))
 
 
+(print (string-rtrim "abc     "))
+(print (string-ltrim "     abc"))
+(print (string-trim "  abc   "))
+
+
 (print "Test ends")
\ No newline at end of file