1. Sprague-Dawley rats were given corticosterone for 4 to 14 d either by subcutaneous injection (50 mg/kg body-weight per d) or as a higher dose in the diet (1 g/kg diet). Energy balance was calculated using the comparative carcass technique. 2. Corticosterone significantly suppressed growth rate by at least 50% (P less than 0.001 in all experiments). The reduction in growth was more marked in males than in females. 3. Hormone treatment significantly reduced metabolizable intake (kJ/d) in males but not in females. Expressed relative to either metabolic body size (kg body-weight0.75) or fat-free mass, metabolizable intake tended to be increased in the treated groups. 4. Energy expenditure, calculated as the difference between metabolizable intake and gain and expressed as kJ/d, did not differ between treated and control rats. Relative to either metabolic body size or fat-free mass, expenditure was consistently increased in treated rats. This change was statistically significant in five of the eight comparisons. 5. The corticosterone-treated rat is characterized by high energy intake and expenditure relative to its body size and growth rate. Alterations in the relative sizes of different lean tissues may contribute to these changes.