Recent correlational studies showed that oxytocin is associated with parenting style in humans as in other mammals. Here the first double-blind, placebo-controlled, within-subject experiment with intranasal oxytocin administration is presented. Subjects were 17 fathers with their toddler, observed in two play sessions of 15. min each with an intervening period of 1 week. In the oxytocin condition fathers were more stimulating of their child's exploration than in the placebo condition, and they tended to show less hostility. Parent training experiments might be combined with intranasal oxytocin administration to test differential and cumulative effects of traditional, interaction-focused versus pharmaceutical treatments.