Preputial gland activity is related to social experience (Hucklebridge, Nowell & Wouters, 1972) and these glands are thought to affect the fighting behaviour of mice through the release of an aggression-promoting pheromone (Mugford & Nowell, 1970). The coagulating glands are thought to be the source of an aggression-inhibiting pheromone (Haug, 1971). The present study provides direct evidence for the function of these glands by assessing the aggression-inducing properties of combinations of the gland secretions with bladder urine or water. A number of 4-month-old male T.O. albino mice were killed. The preputial and coagulating glands were dissected out and the gland contents were gently squeezed into bladder urine or into the same amount of distilled water. Six test substances were used: (1) bladder urine, (2) bladder urine+preputial gland secretion, (3) bladder urine + coagulating gland secretion, (4) water, (5) water + preputial secretion, and (6) water + coagulating gland secretion. The 15 mice used