The rearing of rats at 2 different densities (3 and 40 rats) during 2-3 wk had no effect on their adrenal weight. The adrenal weight was not changed by adrenaline (20 .mu.g/kg) adminstration. The crowding of rats had no effect on corticosterone and aldosterone concentration but resulted in a significant decrease of adrenal blood outflow. In rats from groups of 3 each there was a decrease in the concentration of corticosterone and aldosterone and in the adrenal blood outflow. Epinephrine (20 .mu.g/kg) in some degree induced recovery of the adrenal function in the groups of 3 and of the adrenal blood outflow in the groups of 40 rats. Epinephrine significantly decreased corticosteroid secretion in rats from groups of 40 rats. Epinephrine administration after adrenoreceptor blocking with inderal and dibenamine had different effects on the values of adrenal function. The effect was dependent on the environmental density of the rats.