Synopsis The nitromusk perfume ingredient, musk abrette, has been reported to cause photoallergic reactions in man. The potential of alternative, chemically related, nitromusks to cause photoallergy has been studied using the Colworth guinea-pig photoallergy test. The results showed that, compared with musk ambrette, musk moskene had a weak potential for inducing photoallergy, and that the musks xylene, ketone and tibetene had only very weak potentials. A study of photo-crossreaction to musk ambrette showed that musk moskene was active, musk xylene was weakly active, while the musks ketone and tibetene were inactive. We conclude that musk moskene is likely to be less hazardous for man than musk ambrette, but caution should be used in selection of concentrations for use on sun-exposed skin. The musks xylene, ketone and tibetene are likely, photobiologically, to be acceptable alternatives to musk ambrette. The photoallergic potential of the nitromusks can, probably, be related to chemical structure.