Abstract: Direct information regarding cells located in phase compartments could be obtained by estimation of DNA content of the individual cells. The proportion of ceils in G₁, S, G₂ and M phases may be determined by DNA histogram.By means of Opton scanning microspectrophotometry, DNA content of the single cell was measured with two different methods, i. e. acriflavine-fluorescence and autoradiography-fluorescence. From DNA histogram analysis, the effects of AT-1727 and ICRF-159 on L₁₂₁₀ cell cycle were studied. The two methods were compared and similar results were obtained.One intraperitoneal injection of AT-1727 at the dosage of 50 mg/kg or 25 mg/kg caused significant changes in DNA histogram. AT-1727 induced a redistribution of cells with respect to the phases of the cell cycle and an accumulation of G₂ phase ceils with decrease in S and M phase cells. By microscopic examination, most cells accumulated in G₂ phase exhibited remarkable morphological changes, such as swollen, vacuolated nuclei and karyorrhexis, etc. After ICRF-159 treatment, the progression of G₂ phase cells into M phase was also retarded and led to an accumulation of G₂ phase ceils.