The dipeptide, N-benzyloxycarbonylprolyl-N-aminoalanine isopropylamide, C19H28N4O4, assumes an extended conformation at variance with the beta-folded conformation of its N-amino glycine-containing analogue. The N-amino amide is trans planar and has similar dimensions to the standard peptide group. One of the N-amino H atoms is intramolecularly hydrogen bonded to the C-terminal amide carbonyl group.