Established cell cultures derived from mouse, rat, hamster, cat, and man were examined for the in vitro activities of UDP-glucuronosyl-, phenol sulfo-, and glutathione-S-transferases. The relative activities of the conjugation reactions differed considerably between the various cell lines: Glutathione-S-transferase activities were present in all cell lines with wide variation between different transferase forms. Phenol sulfotransferase was not detectable at all in most of the cell lines tested or was present at very low levels. In contrast, UDP-glucuronosyltransferase activity was expressed in the majority of cultures. Established cultures containing specific combinations of the various types of conjugases should be useful in examining their role in the inactivation and activation of potentially toxic chemicals.