Human peripheral blood lymphocytes of healthy male and female individuals of different age groups were treated with two aqueous doses (0.5 μg and 1.0 μg) of trimethyltin chloride in mitogen stimulated and serum supplemented culture medium for 72 h at 37°C. Chromatid and chromosome types of aberrations were observed to be increased in both treated sets in all age groups. Significant variations were observed between age groups (P < 0.001) and between experimental sets (P < 0.001). Moreover, interaction of chemical and donors age was statistically highly significant (P < 0.05-P < 0.001). However, no linear correlation between the increase of donor's age and aberrations was observed. © 1991.