A urine coating technique has frequently been used to study the urinary aggression-promoting pheromone. Typically mouse fighters are tested against either castrated mice coated with urine collected from animals of a specific treatment or placebo animals. If the fighters show differential reactions to these two groups of animals, it is inferred that there exists a urinary pheromone that induces the discriminatory reaction of fighters. However, it is equally possible that the fighters' reactions are caused by the behavioral changes in the recipients after urine application. Thus the inference of urinary pheomone may not be proper, and at times misleading. The present proposal seeks: (a) to investigate this possible confounding factor by blocking the olfactory channel of the recipients, (b) to investigate the hormonal determinant of the aggression pheromone, and (c) to identify the chemistry of the pheromone.