We have developed a procedure suited for the isolation of metabolites of docetaxel (Taxotere) from human feces. The compounds were extracted from the feces with diethyl ether and further purified by (semipreparative) HPLC. Four metabolic products were obtained in submilligram quantities. Analytical HPLC with photodiode array detection showed that the purity of each compound was higher than 98%. There structures have been characterized by UV absorption and FAB/MS. All four compounds were oxidation products of the tert-butyl group attached to the C13-side chain, and corresponded to structures identified previously. The purified products were used for evaluating their cytotoxic activities against a human ovarian cancer (A2780) and a rat colon cancer (CC531) cell line, and their myelosuppressive effects in a hematopoietic progenitor toxicity assay. Although distinctions in biological activities between the compounds were evident, all metabolites showed a marked reduction in both cytotoxic and myelotoxic properties.