Serum testosterone level was significantly elevated in adult male rats after a single perinatal allylestrenol administration. 2. Benzpyrene treatment of adult rats perinatally treated with allylestrenol, did not cause changes 1 week after benzpyrene treatment, but 3 weeks later an extremely high serum testosterone level was found. 3. In control animals benzpyrene administration in adulthood did not influence the serum testosterone level either 1 or 3 weeks following the treatment.