Previous studies indicate that tris(2-chloroethyl)phosphate (TCP) preferentially produces hippocampal brain lesions in female versus male rats, and the expression of these lesions is inversely related to the in vivo rate of TCP metabolism. In the present studies, TCP (0.17 mM in all incubations) was metabolized in vitro by liver slices and microsomes from human and Fischer 344N rat liver to bis(2-chloroethyl) hydrogen phosphate (BCP), 2-chloroethanol (CE), and three unidentified metabolites. The rate of TCP metabolism by male rat liver microsomes and liver slices was 0.049 nmol/min/mg protein and 2.53 nmol/min/g liver, respectively. TCP metabolism by male rat liver microsomes was inhibited by 10 microM diisopropyl fluorophosphate, 10 microM paraoxon and carbon monoxide. TCP did not appear to be metabolized by female rat liver microsomes, but female rat liver slices metabolized TCP at a rate of 1.51 nmol/min/g liver. TCP was metabolized by male and female rat plasma at a rate of 0.156 and 0.169 nmol/ml plasma, respectively. TCP was metabolized by male and female human liver microsomes at a rate of 0.027 and 0.031 nmol/min/mg protein, respectively. TCP was metabolized by male and female human liver slices at a rate of 1.37 and 1.82 nmol/min/g liver, respectively. BCP and CE were the major metabolites formed in all studies, except for liver slices and microsomes from two human male subjects in which an unidentified metabolite constituted 29 to 38% of the total TCP metabolism. TCP was not metabolized by plasma or whole blood from male or female human subjects. These results support the previously reported sex-specific difference in TCP metabolism by male and female Fischer 344N rats. However, no sex-specific difference in rates of TCP metabolism by male and female human liver microsomes or slices was observed.