hi there, the function fn2ftp(outfile) returns an integer for the type of outfile. I'm not sure how this code of types is defined. would if(fn2ftp(outfile) == efGRO) work as a test wether outfile is .gro? regards -- Christoph Freudenberger Abt. Organische Chemie I AK Siehl - Uni Ulm -Tel: ++49-731-502-2785