Metabolism of adriamycin, an anthracycline antibiotic, was characterized in both rat and rabbit hepatocytes under aerobic conditions. Adriamycin was the predominant fluorescent species within the cell in hepatocytes from both the rat and the rabbit. In the rat hepatocyte, the primary intracellular metabolite was deoxyadriamycin aglycone, while significant levels of deoxyadriamycinol aglycone were also synthesized; little adriamycinol was observed in the cells or the incubation medium. In contrast, in the rabbit hepatocyte, significant levels of adriamycinol as well as deoxyadriamycinol aglycone were formed; deoxyadriamycinol aglycone was the primary intracellular metabolite while low levels of deoxyadriamycin aglycone were observed. The relative formation of deoxyadriamycinol aglycone and deoxyadriamycin aglycone suggests that adriamycinol may be metabolized more effectively to the deoxyaglycone derivative than the parent drug. Conjugates of adriamycin were not observed in hepatocytes from either the rat or the rabbit or in the incubation medium.