PIP: Optimistic evaluation of the safety of vasectomy in spite of apparent absence of deleterious side effects may have been premature. Numerous studies in a variety of vasectomized animal species show that antisperm antibodies develop following vasectomy. In addition, 50% of vasectomized men have been found to have antisperm antibodies following vasectomy. By inference, this would mean a chronic source of antigen-antibody complexes which might lead to extensive vascular pathology, including endothelial damage with consequent acute vasculities and chronic atherosclerosis. A study by Alexander et al. of vasectomized monkeys suggests that the humoral immune response to antigens that often follow vasectomy could enhance diet-induced atherosclerosis. Long-term epidemiological studies of vasectomized men are needed to establish if vascular damage is a consequence of vasectomy. If so, there is an obvious need to eliminate the chronic source of antigen in those already vasectomized.