Ten adolescents took part in a randomized sequential crossover study comparing two insulin regimes: (1) three preprandial injections of soluble insulin from a pen injector plus ultralente given before bed; (2) morning soluble insulin with ultralente, plus two preprandial injections of soluble. Nine patients completed the study. Metabolic profiles were performed at the end of each 3-month treatment period. Glycosylated haemoglobin levels did not fall significantly on either regimen, and there were no differences between the changes in HbA1 concentration on the two regimens. However, blood glucose concentrations tended to be lower with bedtime than with morning ultralente, and were significantly different at 0800 h (13.1 +/- 2.3 mmol/l vs 17.9 +/- 1.9 mmol/l, p less than 0.02) and 1000 h (14.5 +/- 1.4 mmol/l vs 18.6 +/- 0.7 mmol/l, p less than 0.03). Plasma free insulin concentrations were not different. Total daily insulin dose and the proportion of ultralente given in each regimen did not differ. Results indicate that the rise in early morning fasting blood glucose concentrations was less when ultralente was given at bedtime rather than in the morning.