1. Female rats were treated with allylestrenol on the 15th, 17th and 19th days of their pregnancy. 2. Serum testosterone and progesterone level of their three months old offspring were higher than control in males and females, respectively. 3. Serum progesterone levels of females, treated both prenatally and in adulthood, does not differ from control values. Serum testosterone level of males, treated prenatally and in adulthood, is lower than control. 4. One single allylestrenol treatment in adulthood does not make changes in testosterone concentration in males, but progesterone level is elevated in females. 5. Our experiments draw attention to the dangers of prenatal allylestrenol treatments (administered in case of endangered pregnancies) which may have long lasting effects on sexual steroid hormone levels.