Index: src/OFString.h
==================================================================
--- src/OFString.h
+++ src/OFString.h
@@ -373,10 +373,20 @@
  * \param string The string to append
  * \return A new autoreleased OFString with the specified string appended
  */
 - (OFString*)stringByAppendingString: (OFString*)string;
 
+/**
+ * \return The string in uppercase
+ */
+- (OFString*)uppercaseString;
+
+/**
+ * \return The string in lowercase
+ */
+- (OFString*)lowercaseString;
+
 /**
  * Creates a new string by deleting leading whitespaces.
  *
  * \return A new autoreleased OFString with leading whitespaces deleted
  */

Index: src/OFString.m
==================================================================
--- src/OFString.m
+++ src/OFString.m
@@ -1018,10 +1018,42 @@
 	OFMutableString *new;
 
 	new = [OFMutableString stringWithString: self];
 	[new appendString: string_];
 
+	/*
+	 * Class swizzle the string to be immutable. We declared the return type
+	 * to be OFString*, so it can't be modified anyway. But not swizzling it
+	 * would create a real copy each time -[copy] is called.
+	 */
+	new->isa = [OFString class];
+	return new;
+}
+
+- (OFString*)uppercaseString
+{
+	OFMutableString *new;
+
+	new = [OFMutableString stringWithString: self];
+	[new upper];
+
+	/*
+	 * Class swizzle the string to be immutable. We declared the return type
+	 * to be OFString*, so it can't be modified anyway. But not swizzling it
+	 * would create a real copy each time -[copy] is called.
+	 */
+	new->isa = [OFString class];
+	return new;
+}
+
+- (OFString*)lowercaseString
+{
+	OFMutableString *new;
+
+	new = [OFMutableString stringWithString: self];
+	[new lower];
+
 	/*
 	 * Class swizzle the string to be immutable. We declared the return type
 	 * to be OFString*, so it can't be modified anyway. But not swizzling it
 	 * would create a real copy each time -[copy] is called.
 	 */

Index: tests/OFStringTests.m
==================================================================
--- tests/OFStringTests.m
+++ tests/OFStringTests.m
@@ -118,10 +118,16 @@
 	    R([s[1] upper]) && [s[1] isEqual: @"ABC"])
 
 	TEST(@"-[lower]", R([s[0] lower]) && [s[0] isEqual: @"3𝄞1€sät"] &&
 	    R([s[1] lower]) && [s[1] isEqual: @"abc"])
 
+	TEST(@"-[uppercaseString]",
+	    [[s[0] uppercaseString] isEqual: @"3𝄞1€SÄT"])
+
+	TEST(@"-[lowercaseString]", R([s[0] upper]) &&
+	    [[s[0] lowercaseString] isEqual: @"3𝄞1€sät"])
+
 	TEST(@"+[stringWithCString:length:]",
 	    (s[0] = [OFMutableString stringWithCString: "\xEF\xBB\xBF" "foobar"
 					      length: 6]) &&
 	    [s[0] isEqual: @"foo"])