Glucose disposal was studied in six very low birth weight infants (birth weight 1093 +/- 67 g (M +/- SEM), gestational age 29.8 +/- 0.6 weeks, postnatal age 5.2 +/- 0.9 days) by constant infusion steady state technique. All babies required artificial ventilation because of respiratory distress syndrome (four) or aspiration pneumonia (two). Nine healthy prematures of comparable birth weight, gestational age, and postnatal age formed the control group. During a constant glucose infusion at a rate of 8 mg/kg/min (7.7 +/- 0.2) mean blood glucose levels of the sick infants were higher than the corresponding control values. All sick babies had glycosuria (glucose excretion 34 +/- 19 mg/kg/hr compared to none of the controls 0.8 +/- 0.2, p less than 0.01). Glucose disposal in the sick prematures was significantly decreased in comparison to the healthy infants [92.6% (78.7 to 99.3%) of input rate vs. 99.8% (99.7 to 99.9%), p less than 0.01]. It is concluded that sick very low birth weight infants tend to develop hyperglycemia, glucosuria, impaired glucose disposal, and renal caloric wasting when exogenous glucose is supplied at a rate of 8 mg/kg/min, which is usually well tolerated by healthy prematures.