The effect of the intravenous glucose on plasma levels of glucagon and insulin were evaluated in thirty-five LBW preterm infants who were appropriate for gestational age. Their mean birthweight and gestational age were 1220 +/- 55 g (range 750-1730 g) and 29 +/- 1 weeks (range 25-35 weeks), respectively. A 30 min glucose infusion in 16 infants (1 g/kg b.w. in 30 min) caused a prompt and sustained suppression of plasma glucagon and a delayed but significant insulin release. The mean of the sum of maximal plasma glucagon decrements below the baseline was 173 +/- 42 pg/ml. In another 12 infants a significant fall in plasma glucagon and a variable but significant plasma insulin release also occurred throughout the 24 h study on continuous intravenous glucose (rate 2.4-2.7 mg/kg/min). The mean of the sum of maximal plasma glucagon decrements below the baseline up to 12 h was 282 +/- 36 and was similar to that seen in the previous group.