Twenty-four--hour energy expenditure (EE) was measured by indirect calorimetry in 10 body builders and 10 lean control subjects of the same sex with similar age, height, and percent body fat. The study was performed to elucidate possible effects of strength training on energy metabolism and substrate utilization. Twenty-four--hour EE was higher in the body builders than in control subjects but was similar when adjusted for differences in fat-free mass. A higher 24-h nonprotein respiratory quotient (RQ) was found in the body builders. Because both groups were in energy balance, the higher RQ in the body builders can be attributed to a different habitual diet or may be explained by physiological differences.