Cnidarians are the lowest animal group having a nervous system. The primitive nervous systems of cnidarians produce large amounts of a variety of neuropeptides, of which many or perhaps all are amidated at their C terminus. In vertebrates, peptide amidation is catalyzed by two enzymes acting sequentially, peptidyl-glycine alpha-hydroxylating monooxygenase (PHM) and peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL). In mammals both enzymatic activities are contained within a bifunctional protein that is coded for by a single gene. Using PCR and degenerated oligonucleotides derived from conserved regions of PHM, we have now cloned a PHM from the sea anemone Calliactis parasitica showing 42% amino acid sequence identity with rat PHM. Among the conserved (identical) amino acid residues are five histidine and one methionine residue, which bind two Cu2+ atoms that are essential for PHM activity. No cDNA coding for PAL could be identified, suggesting that sea anemone PAL is coded for by a gene that is different from the sea anemone PHM gene, a situation similar to the one found in insects. This is the first report on the molecular cloning of a cnidarian PHM.