The metabolic characteristics of nine postobese and six lean control male individuals were investigated to identify factors potentially associated with the predisposition to become obese. The postobese subjects had been maintaining their body weight stable for at least six months following a 24.8 kg mean weight loss. Body weight, fat mass and fat-free mass were comparable to values of the control subjects. Data obtained in postobese and control subjects were also compared to those of seven obese male individuals whose mean body weight was comparable to the body weight of postobese subjects before they initiated their weight-reducing program. Resting metabolic rate (RMR) was significantly higher (P less than 0.05) in the obese than in the two other groups. Thermic effect of food and participation in physical activities were similar in the three groups of subjects. Daily energy intake tended to be higher in control subjects but not to a statistically significant extent. However, energy intake above RMR was statistically higher in control subjects than in the two other groups. As expected, fasting and postprandial plasma glucose and insulin were substantially higher in obese than in postobese and control subjects. Moreover, fasting and postprandial hyperglucagonemia was observed in both obese and postobese subjects, suggesting that weight loss did not normalize plasma glucagon levels as was the case for glucose and insulin. From an energetic standpoint, results of the present study suggest that people predisposed to obesity may be characterized by reduced energy needs over resting metabolic rate, a phenomenon that would not be explained by a reduced physical activity level.