Recent advances in neonatal care have permitted the survival of very low birth weight infants who are difficult to nourish, and ultimately develop clinical and biochemical signs of malnutrition. These infants may be at greater risk for nosocomial infection than normally nourished hosts. We have compared neutrophil adherence and chemotactic responses in a newborn rat model of protein-calorie malnutrition. Wistar rats at 14 days gestation received either a normal (24% protein) or isocaloric (2.5% protein) diet. On day 5, rat pups were divided into three groups: pups allowed to nurse on their own dam (normal); normally nourished pups foster nursed onto a malnourished mother (depleted); or malnourished pups foster nursed to a normal dam (repleted). Granulocytes from depleted pups demonstrated significantly diminished adherence and chemotaxis when compared to normal or repleted pups. Thus, abnormalities of neutrophil function in malnourished newborn rats may contribute to increased susceptibility to bacterial infection.