Polyoxypeptin, a potent inducer of apoptosis in human pancreatic carcinoma cells, was isolated from an ethyl acetate extract of a Streptomyces culture broth. Structural determination by 2D-NMR and X-ray crystallographic analysis revealed that it is a novel cyclic hexadepsipeptide containing five hydroxylated amino acids. The unusual and hitherto unreported amino acid 3-hydroxy-3-methylproline was one of them.