NCSA xdiff takes two source files and compares them to find just the editing changes you have made between the two versions. Using xfix, part of the package, you can then patch in the changes on a remote machine, saving you the time and trouble of working with an editor on a slow, possibly unreliable transmission line. xdiff.sithqx is a Stuffed, BinHexed file which contains the program, source code and documentation for Macintoshes. You need StuffIt or UnStuffIt 1.5 or later to unpack the file. This source code also works on Unix machines with the included makefile. xdiff.tar contains the source code for xdiff and xfix for unix machines. You should get a printed copy of the documentation because it contains many graphic examples which we cannot provide in text form. A makefile is provided with the proper compile commands. bugs to bugs@ncsa.uiuc.edu comments to softdev@ncsa.uiuc.edu