Abstract The metabolism and cytotoxicity of benzophenone and estrogenic activity of its metabolites have been studied in freshly isolated rat hepatocytes and cultured MCF-7 human breast cancer cells, respectively. The incubation of hepatocytes with benzophenone (0.25–1.0 mM) elicited a concentration- and time-dependent cell death, accompanied by loss of intracellular ATP and depletion of adenine nucleotide pools. Benzophenone at a low-toxic level (0.25 mM) in the hepatocyte suspensions was converted to benzhydrol, p-hydroxybenzophenone and its sulfate conjugate, without marked loss of cell viability. The amounts of benzhydrol and sulfate conjugate increased with time. In contrast, addition of 2,6-dichloro-4-nitrophenol (an inhibitor of sulfotransferase; 0.1 mM), nontoxic to hepatocytes during the incubation period, enhanced benzophenone-induced cytotoxicity, and this effect was accompanied by a decrease in the formation of sulfate conjugate and increase in the amount of free p-hydroxybenzophenone. In another experiment, MCF-7 cells, estrogen-responsible breast cancer cells were cultured in estradiol free medium and then exposed to 10 nM–500 μM benzophenone or its metabolites for 6 days. Although at higher concentrations all the compounds were toxic, except for benzophenone and benzhydrol, 10–100 μM p-hydroxybenzophenone significantly increased cell proliferation. These results indicate that benzophenone is enzymaticaly converted to benzhydrol, p-hydroxybenzophenone and its sulphate conjugate in rat hepatocytes. Even if there is less free p-hydroxybenzophenone than benzhydrol and sulfate conjugate in hepatocyte suspensions, p-hydroxybenzophenone itself acts as a weak xeno-estrogen on MCF-7 cells.