Premature chromosome condensation was induced by cell fusion in stimulated human lymphocytes treated with different cytostatics. Changes in the proportion of the cell-cycle stages were investigated after 72 h of culture. Although it has been reported that some agents which induce severe DNA damage accumulate cells in G2, our results have shown some differences in the modes of action of the different tested chemicals. These variations could be due to several factors like mechanisms of action of the drugs, sensitivity of lymphocyte subpopulations to the cytostatics, inter- and intra-individual variability in the response of donors.