Semi-quantitative estimations of the activities of 65 enzymes were studied for cases of azoospermia in an attempt to correlate the seminal enzyme profile with the origin of the azoospermia. One single enzyme--alpha-glucosidase--showed variation. All other specificities tested gave identical results for all the azoospermic samples and for normal controls. The alpha-glucosidase activity that is present in normal semen was absent from samples from patients with azoospermia associated with a complete obstruction of the genital tract, and also from all semen samples from vasectomized subjects. This enzyme appears to be secreted by the epididymis, and the activity present in azoospermic semen can provide information concerning the origin of the azoospermia and the functional state of the epididymis. Positive but reduced alpha-glucosidase activity appears to be frequently associated with inflammatory disease. The consequences of these findings are discussed.