A genomic region including exons 2 - 11 was replaced with an NLS-lacZ cassette and an FRT flanked neo cassette via homologous recombination. Flp mediated recombination removed the neo cassette. Ceramide synthase activity assays revealed a significant decrease in activity towards C20 acyl-CoA to ~10% in the epidermis and to ~20% in the dermis of homozygous mutant mice. (J:213606)