> The problem with CHAR(16) fields (been there done
> that!) is that you run into problems with special
> characters- e.g. ASCII 0 terminates the string etc.

There used to be a bug with returning ascii 0 from UDF,
but afaict from short test, it has been fixed in FB1.5.2.

> While the database may handle this properly there are
> invariably some bugs in database libraries that
> truncate the field "by accident" (i.e. bug) so it
> really isn't a workable solution.

If you do not mind using UDFs, then just write one function
to generate GUID in binary form, another to convert it
to some nicer, binary-zero-free, printable format.
Do you need anything else ?

Ivan