This study was carried out to investigate the immunopathological effects of 7, 12-Dimethylbenz[a]anthracene(DMBA) on mouse thymus. DMBA was administered subcutaneously to BALB/C mice by interscapular single injection of 50 or 100 ng/g of body weight. Each DMBA treatment group and additional corn oil control group of mice were studied on day 1, 3, 7, 14 and 21 following the injection of DMBA. DMBA treatment resulted in marked decreases in weights and cellularity of thymus. Thymus weights were decreased by 50.6 and 66.0% at 21 days, respectively, after treatment of 50ng/g and 100 ng/g DMBA.