We have used an enzymatic (spectro-photometric) and a flow cytometric (GSH-MBCL) method to compare the glutathione (GSH) content of doxorubicin sensitive (P388) and resistant (P388/R-84) murine leukemic and human lung cancer cells. The flow cytometric analysis revealed that GSH-MBCL conjugate formation was dependent on glutathione-S-transferase (GST) activity. The human solid tumor cell lines exhibited extensive heterogeneity, high GSH content, and GST activity. In contrast to the enzymatic method, the flow cytometric method did not accurately reflect the 95% reduction in GSH content of cells treated for 24 h with 100 microM BSO. Possible reaction of MBCL with other sulfhydryl groups (other than GSH) in BSO-treated cells may be responsible for this discordance. We have also shown the feasibility of using dual parameter flow cytometry to monitor cellular anthracycline (daunorubicin) retention and GSH-MBCL conjugate fluorescence in human tumor cells. These two parameters, which measure drug retention and cellular detoxification, are believed to be the important determinants of chemoresistance in tumor cells.