The frequency of micronuclei (MN), sister chromatid exchange (SCEs), and the proliferating rate index in peripheral blood lymphocytes from 93 individuals were measured. Fifty-two of the individuals were workers in the plastics industry where they were exposed to vinyl chloride monomer while the remaining 41 individuals served as a control group. In our results, an increase of SCEs and MN, as well as inhibited cell kinetics, was observed in the group of exposed workers. Of the tests used, SCE was found to be the most sensitive endpoint for indicating a biological response. However, since methods for restricting the MN analysis to only cells at risk (i.e., second generation interphase cells) were not used, this statement requires verification.