Perfusate from rat livers perfused with benzene (approximately 0.7-7 x 10(-4) M) or trans,trans-muconaldehyde (MUC) (10(-4) M) was extracted and analyzed by reverse-phase HPLC. Based on retention time and co-elution experiments, benzene was found to be metabolized to trans,trans-muconic acid, a urinary ring-opened metabolite of benzene and a major in vivo and in vitro metabolite of MUC. These data demonstrate that benzene ring-opening occurs in the liver. Following perfusion with MUC (a microsomal hematotoxic metabolite of benzene), trans,trans-muconic acid and three other MUC metabolites were detected in the perfusate extract, suggesting that these metabolites would be present in the circulation following metabolism of MUC.