The UDS induction assay with primary hepatocytes as the target cells is a determinative assay for chemical carcinogens. This assay is, however, limited to the availability of freshly prepared liver cells. A cryopreservation technique for liver cells has recently been described. Frozen cells have been shown to retain a variety of enzyme activities essential for xenobiotic metabolism after being thawed. In the present investigation, 19 direct or indirect-acting carcinogens were tested with respect to their capacity to induce DNA repair in primary as well as cryopreserved human and rat hepatocytes. Cryopreserved cells yielded results that were essentially indistinguishable from fresh cells. Only marginal differences were observed between hepatocytes of rat or human origin. These results demonstrate the suitability of cryopreserved hepatocytes as indicator cells for the study of UDS induction to discover possible carcinogenicity in chemicals.