15 preterm infants were treated for recurrent apnoea with theophylline. 5 were given oral choline theophyllinate, but this was erratically absorbed. 14 were given IV aminophylline on 23 occasions. Apparent volume of distribution of theophylline in 12 infants was 0.71 +/- 0.18 1/kg (mean +/- SD). Plasma clearance rate measured in 11 infants at steady state was 18.6 +/- 4.8 ml/kg per hour. Calculations show that a loading dose of 6.2 mg/kg aminophylline intravenously and maintenance of 4.4 mg/kg per day would produce serum levels of between 6 and 12 mg/l in all but one of the infants studied, with no infant having toxic levels.