The structure of the antitumor antibiotic himastatin was determined using a combination of spectroscopic and chemical degradation techniques. Himastatin is a unique dimeric cyclohexadepsipeptide joined through a biphenyl linkage between two oxidized tryptophan units. The gross structure of the dimer was established through degradative ozonolysis. Himastatin consists of D-valine, D-threonine, L-leucine, L-alpha-hydroxyisovaleric acid, (3R,5R)-5-hydroxypiperazic acid, and (2R,3aR,8aR)-3a-hydroxyhexahydropyrrolo[2,3b]indole 2-carboxylic acid subunits.