Cytogenetic changes and cell-cycle kinetics were examined in cultured lymphocytes of 16 workers occupationally exposed to styrene in two styrene workshops, where the styrene concentrations in the air were 2-211 ppm in one and about 30 ppm in the other. The styrene-exposed workers showed no increase in chromosomal aberrations or sister-chromatid exchange frequencies, while a slight decrease in the mitotic index and a slight inhibition of cell growth were detected. No correlation was evident between the cytogenetic findings and styrene exposure intensity as examined by the repeated air analysis, the personal sampling method or the urinalysis for metabolites.