We have isolated and cloned a cDNA for rat pituitary adenylate cyclase activating polypeptide (PACAP) precursor protein from the brain. The nucleotide and the deduced amino acid sequences revealed that the rat PACAP cDNA encoded a 175 amino acid protein highly homologous to the ovine and human PACAP precursors. The rat PACAP precursor protein included a putative signal peptide at the amino-terminus, a PACAP-related peptide (PRP) of 29 amino acid residues and the rat PACAP of 38 amino acid residues flanked by basic processing sites, and a carboxy-teminus amidation signal for PACAP. Furthermore, the amino acid sequence of the rat PACAP was completely identical to that of the ovine and human PACAP. Northern blot analysis of rat brain RNA revealed an approximately 3.0 kb transcript for the PACAP precursor in rat brain.