The concentrations of five steroids in samples of spermatic venous blood collected from 17 men undergoing ligation of varicocoeles were compared with those in samples from the antecubital vein. There was evidence of testicular secretion of testosterone, androstenedione, oestradiol-17 beta and oestrone, since the ratios of the mean concentrations in spermatic venous plasma to those in peripheral venous plasma were 77.2, 9.1, 28.7 and 1.6 respectively. The testicular secretion of oestrone sulphate was minimal; the ratio of the mean concentrations in spermatic and peripheral plasma was 1.07. These results support the view derived from isotope dilution studies that almost all oestrone and oestrone sulphate in the circulation is derived from peripheral conversion of other precursor steroids.