This work describes a simple and reproducible method of determining the fructose content of sperm in order to assess the impregnation of the genital tract with testosterone in men in whom spermatogenesis is blocked by a combination of progesterone and androgens. The colorimetric method of Karvonen and Malm was used with certain modification. The fructose content of sperm is colorimetrically determined by the indol in a concentrated chlorhydric milieu, after deproteinization by cadmium hydroxide. Instructions are given for preparation of the aqueous solution of indol, the sulfuric solution of cadmium sulfate and the fructose solution, as well as for the procedure itself and calculation of the fructose concentration. The method was designed to monitor men taking 20 mg/daily of medroxyprogesterone acetate and applying testosterone daily to the torso. The progesterone inhibits spermatogenesis in inhibiting follicle stimulating hormone and luteinizing hormone and also blocks testosterone secretion by the testicles. The addition of testosterone is designed to maintain a normal level of testosterone to avoid feminization.