The capacity of malnourished infants to produce interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) was evaluated before and after nutritional rehabilitation. Ten marasmic patients without infectious diseases 2 to 8 months of age with -2.48±0.54 weight for age Z score (mean ± SD) were studied on admission, and after 4 month of nutritional therapy in a Closed Nutritional Recovery Center. Cytokines were induced by in vitro stimulation of blood mononuclear cells with lipopolysaccharide. IL-1β and TNF-α were determined in supernatants and cell lysates using an specific immunoassay. Low levels of released and cell-associated IL-1β were found on admission; mean±SEM values were 2.0±0.5 and 1.3±0.5 ng/ml, respectively. After nutritional rehabilitation, a significant increase of released and cell-associated IL-1β were observed: 5.4±0.8 and 3.7±0.3 ng/ml, (mean±SEM) respectively, p<0.01, paired t test. A significant increase in TNF-α production was observed in 8 of 10 infants after nutritional rehabilitation (p<0.02, paired t test). The diminished production of IL-1ß and TNF-α may be one of the mechanism by which protein calorie malnutrition leads to impaired immunocompetence and increased susceptibility to infectious diseases.