As toluene is an organic solvent, its cytotoxic effect on the cell is known. Similarly, it has been demonstrated that many of the chemical agents that enter the body through smoking have cytotoxic and genotoxic effects on the cells. In this study, the effects of these two toxic agents,both separately and in combination, on leukocyte counts, lymphocyte counts and mitotic index values are investigated. The study was carried out on blood samples of 100 males, divided into four groups: 25 non-smokers and 25 smokers, 25 toluene-exposed non-smokers and 26 no toluene-exposed smokers. The blood cell values of the blood samples were determine automatically on the hemogram apparatus. In addition slides of the blood samples were prepared according to the chromosome analysis procedure and the mitotic index values were determined through microscopy. The possible effects of smoking and toluene on lymphocyte life span was considered by correlating mitotic index values with lymphocyte counts in the same way for each of the subgroups. Results revealed that leukocyte counts and mitotic index values were higher in the smokers than the non-smokers whether or not they had been exposed to toluene. In addition the results indicate that lymphocyte life span may be shortened due to cigarette smoking and toluene exposure.