The significance of BrdU/DNA double staining method using flow cytometry as a chemosensitivity test of anticancer agents is herein reported. Experimentally, CDDP, ADM and MMC yielded a significant increase of G2 phase fraction at 24, 48 and 72 hours, and caused a significant decrease of BrdU labeling index at 48 hours. The changes of G2 phase fraction and BrdU labeling index were correlated well with the result of colony forming test, and, therefore, were considered as a useful index of lethal effect of anticancer agents. For the clinical application, enzymatic preparation and discontinuous Ficoll density gradient method might be advantageous to collect viable tumor cells from solid specimen. Flow cytometric BrdU/DNA assay can be clinically applied as a chemosensitivity test in selecting effective anticancer drugs.