1. Male, albino, Sprague Dawley rats underwent surgical cingulotomy or sham operation and were then implanted with subcutaneous morphine pellets or exposed to forced running. 2. The conditions of cingulotomy or forced running alone did not cause a significant increase in plasma i.r. Beta endorphin concentrations. 3. The combined treatment of cingulotomy plus forced running caused a significant elevation of plasma beta-endorphin concentrations. 4. The cingulum is involved in the elicitation of stress hormone responses in the rat.