Abstract: By means of autoradiographic method, the cytokinetic effects of bimolane(AT-1727) on S₁₈₀ cells were studied. After pulse labelling S₁₈₀ Cells with ³H-TdR, one intraperitoneal injection of bimolane at the dose of 50 mg/kg caused gradual decrease of labelling index. After 24 hours of treatment, the labelling index dropped from 31.1% to 14.5%.After pulse labelling with ³H-TdR and blocking the S₁₈₀ cells in metaphase by colchicine, ip injection of bimolane at the same dose significantly decreased the percentage of labelling mitosis (PLM). These results suggest that bimolane could damage the S phase cells and prevent the cell progression from S phase to M phase. By treatment with bimoiane, the mitotic index decreased, mitotic cells underwent a remarkable damage (such as pyknosis and adhesion of the chromosomes etc) and the S₁₈₀ cells were blocked in the metaphase.Experiments also showed that bimolane retarded the progression of G₂ phase into M phase. The incorporation of ³H-TdR into DNA was inhibited significantly after 6 hours of injection of bimolane.With the continuous labelling technique by ³H-TdR for 14 hours, it was demonstrated that the fraction of cells in G₀ phase was about 50%. Nine hours after the administration of bimolane, the damaged cells in G₀ phase Were about 8%, which was not significantly different from that of the control group.From these data it would appear that bimolane may be classified as a cell cycle specific agent.