(C57BL/6 X A/J) F1, (SWR/J X A/J) F1 and BALB/cBy mice, thymectomized on Day 3 (D3TX) or Day 7 (D7TX) or sham thymectomized (STX), were studied for immunopathologic changes in the ovary, testis, and gastric wall. In 95% of B6AF1, 100% of SWRAF1, and 35% of BALB/cBy mice ovarian disease developed, with onset at 5-6 weeks of age. Ovarian disease was not found in D7TX or STX mice. In D3TX mice, it was associated with mononuclear infiltration and ovarian follicle destruction, leading to atrophy. Epididymovasitis was detected in 70-90% of SWRAF1, 50% of B6AF1, and 64% of BALB/cBy mice after D3TX; whereas orchitis occurred in about 20% of SWRAF1 and B6AF1 mice. In some mice epididymovasitis also developed after D7TX, but not after STX. In contrast to the negative immunohistochemical findings in diseased ovaries, typical immune complex-like deposits of mouse IgG were detected by immunofluorescence along the basement membrane of epididymal ducts and seminiferous tubules. However, maximum incidence of epididymitis preceded immune complex detection. Gastritis developed in both female (57%) and male (50%) BALB/cBy mice after D3TX, occasionally after D7TX, but not after STX. Gastric mucosa was hypertrophic with dilated glands and heavy lymphocytic infiltrations throughout all gastric layers. BALB/cBy mice with gastritis usually did not have disease in the gonads, and vice versa. This study, therefore, confirms and extends the findings of Nishizuka and colleagues.