Data on cigarette smoking, testicular varicoceles, seminal fluid indexes, and oligospermia were examined in 160 young men without known disease and in 94 husbands in infertile couples. The combination of smoking and testicular varicoceles is strongly related to the incidence of oligospermia, defined as sperm count less than or equal to 20 X 10(6)/ml, in each sample. Smokers with testicular varicoceles, in each sample, had a disproportionately high incidence of oligospermia. In the combined sample of 254 men, the smokers with testicular varicoceles had an incidence of oligospermia approximately ten times greater than that in nonsmokers with testicular varicoceles and approximately five times greater than that in men who smoked but were without testicular varicoceles. This relationship of cigarette smoking and testicular varicoceles to oligospermia has not been previously reported. The pathophysiologic basis of the interaction between smoking and varicoceles was theorized to be due to an increased secretion of catecholamines from the adrenal medulla, induced by cigarette smoking. The elevated catecholamine concentrations in the renal vein would then reach the testes via retrograde flow down the internal spermatic vein in men with testicular varicoceles, resulting in seminiferous tubule damage.