This study was carried out to investigate the immunopathological effects of 7,12-Dimethylbenz[a]anthracene(DMBA) on spleen in mice. DMBA was administered subcutaneously to BALB/C mice by interscapular single injection of 50 or 100${mu}g/g$ 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 decrease in weights and cellularity of spleen. Spleen weights showed the greatest decrease at 14days after 50${mu}g/g$ DMBA treatment, and at 21days after 100${mu}g/g$ DMBA treatment. Spleen cellularity was similarly deceased in comparison with spleen weights. Spleen showed morphologically no typical changes throughout the experiment after 50${mu}g/g$ DMBA treatment. Following the treatment of 100${mu}g/g$ DMBA the spleen showed severe fibrosis, hemosiderin precipitation, and megakaryocytes decrease in red pulp at 14 days, while hemopoietic function was partly restored in addition to the appearance of a few megakaryocytes at 21 days. In spleen sections treated with antibodies to IgM or Thy1.2, lymphocytes strongly stained with IgM antibody were infiltrated around the central artery within the white pulp, and T-lymphocytes of periarterial lymphatic sheath (PALS) were diminished and destructed in sections treated with Thy1.2 antibody, at 14 days after the treatment of 100${mu}g/g$ DMBA. By the electron microscopy phagocytic epithelial cells or macrophages were remarkably increased in spleen at 14and 21days following the treatment of 100${mu}g/g$ DMBA.