Over a three-year period, 12 infants received dextrose/insulin infusions for severe hyperkalaemia from a mean age of 24 h. The infants were born after 24 to 26 weeks of gestation and weighed 730 +/- 172 g (mean +/- SD) at birth. Serum potassium concentration ranged from 7.4 to 8.4 mmol/l (7.7 +/- 0.4 mmol/l; mean +/- SD). Four had cardiac arrhythmias. All infants showed an initial response, serum potassium concentration decreased below 6.5 mmol/l in 5 +/- 2 h. In two infants, rebound hyperkalaemia occurred and was resistant to treatment; both infants died, one during an exchange transfusion. In the other 10 infants, infusions were ceased at a mean postnatal age of 53 h. Hyperglycaemia was the major problem during infusion and was resistant to increases in insulin concentrations. Normoglycaemia was achieved in 10 infants. The hypertonic solution consisted of a dextrose/insulin ratio of 2.2 +/- 0.6 g/IU, which delivered glucose at a rate of 0.46 +/- 0.15 g/kg/h, in addition to the pre-existing stable maintenance glucose intake.