The frequency of sister chromatid exchanges (SCE) and micronuclei in peripheral blood lymphocytes was evaluated in 48 agricultural workers and 50 control subjects living in central Italy. No difference in SCE frequency was found between the control and the exposed populations with respect to age, smoking habits, and duration of exposure, although smokers, both farmers and controls, had a higher SCE frequency than nonsmokers. However, the comparison of proliferative rate index values found in the two groups revealed a significant decrease in the activation capability of lymphocytes in the pesticide-exposed workers, probably related to the toxic properties of chemicals to which the farmers were exposed. On the contrary, the analysis of micronuclei frequency indicated that there were differences between the exposed and control subjects with respect to smoking habits, age, and duration of exposure. Our results indicate that, in the study population occupationally exposed to a complex mixture, including insecticides, fungicides, and herbicides, there is clear, although slight, evidence of clastogenic activity in peripheral blood lymphocytes but no corresponding effects on SCE induction. Moreover, our data show clear evidence of cell proliferation delay relatable to chemical compounds used in agriculture.