The investigation has been carried out on cultures grown in the presence of 5 x 10(-1) - 5 x 10(-5) M acrylonitrile with or without a rat liver metabolizing system (S-9 mix). The results obtained showed that acrylonitrile was toxic starting from the 5 x 10(-3) M concentration, caused a significant increase in the sister chromatid exchange (SCE) frequency in comparison with the controls (p less than or equal to 0.001) when the concentration was 5 x 10(-4) M, and elicited reparative deoxyribonucleic acid (DNA) synthesis, determined by tritiated thymidine uptake, particularly when the concentration was 5 x 10(-1) M. These effects were observed in lymphocytes of different donors and after drug activation by the S-9 mix metabolizing system.