Styrene and 11 styrene analogues were tested for their ability to induce sister-chromatid exchanges (SCEs) by a 48-h treatment in human whole-blood lymphocyte cultures (72 h). Styrene, its methyl-substituted derivatives (substituted at 2-, 3-, 4-, 3,5- or beta-position) and two styrene oxides (3,5-dimethylstyrene-7,8-oxide and 4-nitrostyrene-7,8-oxide) induced a distinct dose-dependent increase in SCEs. Also, 4-methylstyrene-7,8-oxide and alpha-methylstyrene showed a positive effect, but were not able to double the mean number of SCEs/cell at the concentration ranges available. Ethylbenzene had a marginal effect on SCEs at the highest dose tested. 2-Phenylethanol did not increase SCEs. The results indicate that styrene and methylstyrenes are converted into reactive metabolites in the whole-blood lymphocyte cultures. The negative or weak effects of styrene analogues without a double bond in the side-chain (ethylbenzene and 2-phenylethanol) suggest that the reactive metabolites are derived from the conversion of the vinyl group and are styrene-7,8-oxides.