The purpose of this study was to aid in the prediction of tumor cell tolerance to radiotherapy and/or chomotherapy . For this study, cell surviving curves were obtained for mouse lymphoma YAC-1 cell line using semiautomated MTT assay. 2, 4, 6, 8, 10Gy were irradiated at a dose rate of 210cGy/min using 60Co Irradiator ALDORADO 8. After irra diation, YAC-1 cell lines(3X10(4) cells/ml) were exposed to bleomycin or cisplatin for 1 hour. The viable cells were determined for each radiation dose and/or each concentration of drug at the 4th day. And they w ere compared to control values. The obtained results were as follows: 1. The surviving curve with gentle slope was obtained after irradiation of 2, 4, 6, 8, 10Gy on YAC-1 cell line. 2. The cytotoxicity of bleomycin or cisplatin was increased significantly at all concentration of 0.2microgram/ml, microgram/ml an d 20microgram/ml on YAC-1 cell line (P<0.01). 3. There were no significant differences of surviving fractions among 4Gy, 6Gy, and 8Gy after irradiation of each radia tion dose with 2microgram/ml of bleomycin compared with irradiation only on YAC-1 cell line(P<0.05). 5. There were significant differences of surviving fractions between the groups of irradiation only and the groups of i rradiation with 2microgram/ml of bleomycin or cisplatin at all doses of 2, 4, 6, 8 and 10Gy on YAC-1 cell line(P<0.05).