Various types of human gynecological cultured tumor cells were tested for the sensitivity to Peplomycin (PEP), an effective antitumor antibiotic for squamous cell carcinomas, by the regrowth assay method together with morphological observation. Bleomycin-hydrolase activity of these cell lines was also compared in cell-free extracts by assaying the conversion of Bleomycin into its deamidated from (HPLC method). SKG-I, SKG-II, SKG-IIIb cells derived from squamous cell carcinoma of the cervix and RKN cells derived from myosarcoma of the ovary were much more sensitive to PEP than other cell lines. PEP was found to be mainly a time-dependent drug, but also concentration dependent. The effect of PEP on cell morphology was characterized by the appearance of enlarged cells and swelling nuclei. The specific activities of Bleomycin-hydrolase in SKG-I, SKG-II, SKG-IIIb cells were shown to be relatively lower than that in other cell lines. These results suggested that cervical squamous carcinoma cells and ovarian myosarcoma cells were sensitive to PEP and Bleomycin-hydrolase activity was one of factors which decided the PEP sensitivity of human cultured tumor cells.