NSString *string = [myString stringByReplacingOccurrencesOfString:@"<wow>" withString:someString];
Both dasblinkenlight’s and Matthias’s answers will work, but they both result in the creation of a couple of intermediate NSStrings; that’s not really a problem if you’re not doing this operation often, but a better approach would look like this.
NSMutableString *myStringMut = [[myString mutableCopy] autorelease]; [myStringMut replaceOccurrencesOfString:@"a" withString:somethingElse]; [myStringMut replaceOccurrencesOfString:@"b" withString:somethingElseElse]; // etc.
You can then use
myStringMut as you would’ve used
myString, since NSMutableString is an NSString subclass.