In vitro tests were performed to assess the sensitivity to six anticancer agents-ACT-D, ADM, CDDP, CQ, 5-FU and MMC-of a JOHYL-1 (ascites type) cell line from human dysgerminoma which was used as challenge strain. For comparative assessment, anticancer sensitivity was expressed as the ratio of IC50 and IC90 to LD50 (i.v.) in mice. Drug dose-response and time-response curves were plotted, and the IC50 ratio was calculated, for each test compound in order to investigate the mechanism of anticancer action. The results obtained were as follows. CQ proved to be remarkably active and ADM fairly active against JOHYL-1 (ascites), but 5-FU, CDDP and MMC varied remarkably with the parameter of measurement employed. Analysis of IC50 ratio data and patterns of cell growth inhibition indicated the growth-inhibitory effect of CDDP to be concentration-and time-dependent. The results of the present study are in close accord with the pattern of action reported in the literature.