Abstract The administration of 100 μg and 50 μg of estradiol benzoate for 5 consecutive days to adult, nulliparous. Rockland-Swiss mice that previously exhibited maternal behavior resulted in a loss of such behavior. The effect of estradiol was temporary since normal maternal activities were exhibited when the animals were retested two weeks after the termination of hormone treatment. Treatment with 5 μg and 0.5 μg estradiol benzoate did not significantly affect maternal behavior. Progesterone treatment at dosages of 1000 μg and 500 μg was without affect.