The increase in systolic pressure with age, which is observed in some but not all human populations, is believed to be a response to repeated symbolic stimuli arising from the social environment. An attempt was made to simulate these conditions in experimental animals by playing on their inborn drives for territory, survival, and reproduction. Meaningful stimuli were presented to CBA mice in a series of long-term experiments. The methods involved (1) mixing of animals previously maintained in different boxes, (2) aggregation in small boxes, (3) subjecting groups to threat from a predator, and (4) inducing conflict for territory by placing equal numbers of males and females in an interconnected box system. In the experimental situations involving the most severe psychosocial stimulation, the mean arterial blood pressure rose from 126 mm. Hg to the range 150–160; it was sustained at these higher levels for 6–9 months. Those aggregated from birth showed less pressure elevation (to the range 140–150). Blood pressures in females were in the same range as those of males that had been aggregated from birth, but castrates showed minimal effects. Ether anesthesia did not abolish a sustained pressure rise, but the persistently elevated pressure of threatened animals returned to the normal range when reserpine was given. The study demonstrated that social groupings of nonprimates can be used in the experimental approach to the role of psychosocial stimuli and the early environment in the etiology of human hypertension.