Circulating leptin levels, proinflammatory and T helper cells type 1 (Th1), Th2 cytokine production, and lymphoproliferative response were measured in 15 infants with primary moderate protein calorie malnutrition on admission and after recovery of 10% of weight. Sixteen healthy, well nourished infants of comparable age served as controls. A significant deficit in the z-score of weight for age, weight for height, body mass index, and circulating leptin and growth factors were detected in malnourished infants on admission compared with controls (P < 0.05). These deficits were associated with a significant suppression of the lymphoproliferative response, Th1, and proinflammatory cytokine production (P < 0.05). After a 10% weight gain, a significant increase in circulating leptin levels was produced in parallel with a significant increase in Th1 activity, as revealed by an enhancement in interferon-γ and a suppression in IL-4 production. Concomitantly, the lymphoproliferative response became similar to that detected in control infants. Furthermore, a significant increase in IL-1 and TNFα production compared with that at admission was shown. These findings suggest an association between the increase in leptin and the immunological recovery observed following refeeding of malnourished infants.