The serum and seminal plasma concentrations of androstenedione, testosterone, dihydrotestosterone and 17beta-oestradiol were investigated in hypo- and oligospermic males during clomiphene-citrate, administration. A significant increase was demonstrated in the serum testosterone, dihydrosterone and 17beta-oestradiol values, mainly in the first month of therapy. The steroid increase in the ejaculate was less pronounced. Measuring of 17beta-oestradiol in serum appears to be a useful parameter for estimating the stimulative effect of clomiphene citrate.