Metalloproteases of the M13 subfamily, comprising namely neprylisin (NEP) and endothelin-converting enzyme (ECE), are involved in the metabolism of various neuronal and hormonal peptides, and inhibitors thereof have already Zed to therapeutically useful agents. Using homology cloning, we have identified a new member of this family in rat tissues. It is a glycosylated, type II integral membrane protein of 774 amino acids, containing a zinc-binding consensus motif, highly homologous to NEP and, therefore, designated NEPII. We have characterized multiple splice variants of NEPII mRNA with distinct expression patterns in brain regions, pituitary and testis. In situ hybridization of testis, where levels of the NEPII gene transcript are the highest, reveals a localization within round spermatids. In brain, NEPII is expressed heterogeneously among several neuronal populations and according to a pattern grossly complementary to that of NEP.