The relationship between alterations in testicular histology and antisperm antibodies in immature and mature Lewis rats subjected to unilateral vasectomy was studied. Forty percent of immature rats and 90% of mature rats (p < 0.01) demonstrated significant alterations in both the obstructed (vasectomy) testis and the contralateral testis. There were significant changes in antisperm antibodies (ELISA) in the animals which demonstrated histologic changes.