nmd, a novel gene, was isolated by applying the differential mRNA display method to human melanoma cell lines with different metastatic capacity. In a panel of 17 other human tumor cell lines, nmd RNA expression could only be detected at low levels in T24 (bladder carcinoma) and Caco-2 (colon adenocarcinoma). Furthermore, it was found in placenta and liver, but not in skin, colon, spleen, lung, muscle, prostate and kidney. Sequence analysis classified the nmd gene product as a new member of the enzyme family of lipases (almost 30% identity in amino acid sequence with other human lipases). Active site residues of lipases were conserved in NMD, but NMD lacks the regulatory lid domain, which controls entry to the active site in classical lipases. A similar deletion was earlier reported by others in the guinea pig pancreatic (phospho)lipase GPLRP2 and the phospholipase A1 from hornet venom (DolmI).