One hundred twenty-four prepuberal crossbred pigs were used in a series of behavioral bioassays to determine the minimum dose of androstenone (5 alpha-androst-16-en-3-one) that would reduce the level of agonistic behavior among dyads of newly regrouped pigs. Randomly selected females and castrated males were used in 21-h videotaped observation periods. In Exp. 1, isopropyl alcohol was tested against no aerosol to determine if the vehicle (isopropyl alcohol) influenced agonistic behavior. Level of submissive and aggressive behaviors were similar (P greater than .10) between treatments. In Exp. 2, vehicle or androstenone in vehicle was sprayed on the snout and head of both pigs at the start of the encounter. Four bioassays were performed with four levels (.05, .5, 5 and 50 micrograms/pig) of androstenone dissolved in isopropyl alcohol. Sprayed isopropyl alcohol served as a control. At concentrations of .5 and 5 micrograms/pig, androstenone reduced aggressive behavior (P less than .05). Androstenone had no consistent effect on submissive behavior. In Exp. 3, androstenone was sprayed on pigs at the start of the encounter and again at 30, 60 and 90 min after pairs of pigs were mixed. Repeated application of this androgen resulted in levels of agonistic behavior similar to those recorded when nothing was applied (P greater than .10). A single application of as little as .5 micrograms androstenone per pig reduced aggressive behavior among prepuberal pigs and, therefore, may be a way of reducing fighting among newly regrouped prepuberal pigs.