Steroid treatment protocol for the father and paired male conditions. A total of 16 males received estradiol treatment (i.e., vehicle, low dose, high dose) on 3 different months, 2–3 months apart, and an additional 16 males (father and paired males) received the testosterone treatment (vehicle, low, high dose) on 3 different months, 2–3 months apart. Males were tested under each treatment with the vocal control and the infant distress stimulus three days apart.