Twelve infants with underlying gastrointestinal tract disorders receiving 16 courses of total parenteral nutrition were retrospectively studied. Statification according to calorie intake provided the best means for discriminating among different outcomes. Infants receiving greater than 110 calories/kg/d experienced significantly greater increases in weight, mid-arm muscle circumference, and triceps and subscapular skinfold thicknesses than did infants receiving less than 110 calories/kg/d. Catch-up growth was only seen in infants with intakes of greater than 110 calories/kg/d. In nine of these 12 infants, in vitro cellular immune parameters were assayed. Infants in both the high- and low-calorie groups experienced similar increases in transformational responses to pokeweed mitogen (PWM) and phytohemagglutinin (PHA) and in the percentage of peripheral blood T lymphocytes. No increase in serum albumin was seen regardless of calorie intake.