Effect of immunization of male rabbits against androstenedione

After active immunization of male rabbits against androstenedione and with increasing antibody titre the concentration of androstenedione and testosterone in peripheral blood increased more than 1000-fold resp. 20-fold above values of control animals. On histological examination of the testes a marked Leydig's cell hyperplasia was found, though there was no difference in testis weight.