In order to examine the effects of hippocampal lesions on plasma corticosterone levels and ulcer formation, 4 conditions were studied: (1) unrestrained nondeprived (2) unrestrained 24 h food-deprived (3) simple restraint and (4) restraint plus intermittent shock. In the unrestrained and unrestrained plus 24 h food-deprived conditions, neither animals with hippocampal lesions nor control animals developed ulcers. In both instances plasma corticosterone levels were similar in experimental and control animals. Differences appeared in the simple restraint and restraint plus intermittent shock conditions. In both of these conditions animals with hippocampal lesions developed more ulcers and had a higher corticosterone level than controls. It is concluded that animals with hippocampal lesions show an enhanced reaction to stress.