Flow cytometric analyses were done in cervical squamous cell carcinoma cell line (SKG-IIIa) and in cancer cells of cervical cancer cases treated with CDDP using monoclonal antibody of BrdU. 1) In fundamental studies using culture system, accumulation of late S phase cells and of mid S phase cells was observed after 48 hours at the dose of 0.2 micrograms/ml and 0.5 micrograms/ml of CDDP, respectively. 2) Accumulation of early S phase cells was observed at the condition of 1 microgram/ml and 3 micrograms/ml of CDDP. All S phase cells decreased gradually thereafter 3) In clinical studies, accumulation of early S phase cells was observed in cancer cells of cervical cancer cases after intra-arterial infusion of CDDP. However, cell cycle recycling was observed in tumor cells which retained their low sensitivity to CDDP after 21-day treatment with intra-arterial infusion of CDDP.