Androstadienone is the most prominent androstene present on male human axillary hair and on the male axillary skin surface. We have previously shown that this volatile steroid is able to stimulate [corrected] the human female vomeronasal organ in picogram (pg) quantities, resulting in changes in autonomic activity. These effects are gender-specific. The purpose of the present study was to ascertain whether androstadienone could be considered a human pheromone by altering behavior as well as autonomic function. Forty normal female subjects were randomized in a double-blind manner to receive either control or 100 pg of androstadienone directly to the vomeronasal organ. We report that administration of this steroid under these conditions results in a significant reduction of nervousness, tension and other negative feeling states. Concordant changes were observed in autonomic physiology.