Musk xylene (CAS no. 81-15-2), a synthetic musk fragrance ingredient, was evaluated in a battery of short-term genotoxicity tests that included the mouse lymphoma assay, an in vitro cytogenetics assay in Chinese hamster ovary (CHO) cells, the in vitro unscheduled DNA synthesis (UDS) assay in primary rat hepatocytes and an in vivo UDS assay. Musk xylene gave uniformly negative results in these genotoxicity tests. These observation, combined with previously reported negative Ames tests, suggest a non-genotoxic mechanism for the induction of mouse liver tumours by musk xylene.