In order to provide information on the endocrine effects of vasectomy, unconjugated pregnenolone, dehydroepiandrosterone, androstenedione, testosterone, dihydrotestosterone, oestrone and oestradiol were analysed in the blood plasma of twenty Mexican men on two occasions before and 1, 3, 6 and 12 months after vasectomy. Vasectomy appeared to be associated with a significant decrease in the plasma levels of pregnenolone, dehydroepiandrosterone and androstenedione and a significant increase in the levels of dihydrotestosterone and oestrone. A probably significant increase in oestradiol levels took place 12 months after vasectomy but not before. No consistent changes were found in testosterone (up to 12 months) or in FSH and LH levels (up to 6 months) after vasectomy. The unconjugated steroids indicated above, except oestrone, were also estimated, whenever possible, in seminal plasma specimens obtained from thirty-nine subjects (including the twenty indicated above) on the same occasions. Vasectomy was associated with a highly significant decrease of seminal plasma dihydrotestosterone levels on all occasions and a significant decrease in androstenedione levels after 6 and 12 months. After 12 months there was a decrease in dehydroepiandrosterone and an increase in oestradiol; these changes were both probably significant. In another preliminary study, the levels of pregnenolone sulphate, dehydroepiandrosterone sulphate, testosterone glucuronide, testosterone sulphate and dihydrotestosterone sulphate were estimated before and 1 month after vasectomy in the seminal plasma of fourteen to seventeen subjects. Testosterone glucuronide fell, probably significantly, but other conjugates were unchanged. The data indicate that vasectomy may be associated with significant changes in the circulating and in seminal plasma levels of several steroids. The gradual nature of some of the changes observed suggests the necessity of conducting in several centres large-scale, long-term studies on vasectomized subjects and on a carefully matched control group. During the last decade vasectomy has been widely practised in several parts of the world as a method of fertility control. However, information on the endocrine effects of this intervention appears to be scanty. In most of the human studies reported, a small number of individuals were investigated and the studies have been confined to the assessment of the short-term effects of the operation. Moreover, the hormonal indices assessed by the various investigators have been limited, in most cases, to gonadotrophins and testosterone in blood. The present study was designed to assess in the same subjects the levels of a number of unconjugated steroids, FSH and LH on two occasions before and 1, 3, 6 and 12 months after vasectomy. The studies were extended to include steroid analyses in seminal plasma in the hope that such assays might yield information as to the effects of vasectomy on the distribution of steroids in the fluids of the male reproductive tract.
