I've been thinking a little more about using compressed files. How about this: Current OpenSave functions would continue to work much as they do now, except that appropriate .gz files would also be listed in the browser, and possibly returned in the list of paths. Instead of opening returned paths with the built-in open, you would instead use a function in OpenSave (osOpen?) that would check for possible compression and return an appropriate file-like object. For contexts where an uncompressed file path is needed (e.g. handing off to PDBio [for now]), there would be another function in OpenSave that takes a path and returns a corresponding path to a uncompressed file [a no-op if the file was already uncompressed]. Any temporary uncompressed files would automatically be deleted on APPQUIT. Opinions? --Eric