By screening public databases, we identified human and mouse genomic DNA clones that encode the tuberoinfundibular peptide of 39 residues (TIP39). The TIP39 precursor is encoded by at least three exons; a noncoding exon U1, exon 1 encoding residues -61 (initiator methionine) to -19 of the leader sequence, and exon 2 encoding residues -18 to -1 and residues +1 to +39. Secreted human TIP39 is identical to the previously isolated bovine TIP39, whereas mouse TIP39 differs by four amino acids. Phylogenetic analyses suggested that TIP39, PTH, and PTHrP may have evolved from a common ancestor. Synthetic human and mouse TIP39 showed indistinguishable potencies [EC(50): 0.54 (human) vs. 0.74 nM (mouse)] at the human PTH2-receptor stably expressed in LLCPK(1) cells; furthermore, TIP-(9-39) was an inhibitor of cAMP accumulation stimulated by either [Tyr(34)]PTH(1-34)amide or human/bovine TIP39. In the mouse, an approximately 4.5-kb mRNA encoding TIP39 was identified by Northern blot analysis in testis and, less abundantly, in liver and kidney, whereas other tissues revealed additional smaller transcripts. In situ hybridizations revealed TIP39 expression in seminiferous tubuli and several brain regions, including nucleus ruber, nucleus centralis pontis, and nucleus subparafascicularis thalami. Because PTH2 receptor expression was previously shown to be highest in brain, pancreas, and testis, our findings are consistent with the notion that TIP39 is a neuropeptide which may also have a role in spermatogenesis.