Musk ketone, musk xylene, musk tibetene and moskene, synthetic musks used in fragrances, were applied dermally to rats in daily doses of 240 (musk ketone and musk xylene only), 75, 24 or 7.5 mg/kg body weight for 90 days. The chemically related musk ambrette, a known neurotoxin in rats, was used as a positive control. While musk ambrette was clearly neurotoxic and caused testicular atrophy, as had been previously reported, the other compounds tested caused neither effect. The only effects of application of these materials were some organ weight changes at the higher doses, but these were not associated with histopathological changes in any of the tissues. The no-effect levels were: musk ketone, 75 mg/kg for males and females; musk xylene, 75 mg/kg for males and 24 mg/kg for females; moskene, 24 mg/kg for males and 75 mg/kg (highest dose administered) for females; and musk tibetene, 75 mg/kg (highest dose) for males and females.