A newly developed laboratory bioassay procedure showed that male boll weevils, Anthonomus grandis Boheman, produce an air-borne pheromone that is attractive to females. In 1- and 16-hour tests when weevils were preconditioned by 3 different treatments, significantly more females responded to males than to females. When callow adult weevils were removed from the rearing medium before they made contact with other insects, response of females to males increased significantly over those having such contact. In 1-hour tests a slight response of males to males was observed and significantly fewer males responded to females than to other males.