Ten diabetic adolescents who had poor blood glucose control during the preceding year were recruited into a crossover insulin dosage study. Diabetic control was assessed on two insulin dosage regimens; either 1.0 U/kg/day ("limited dosage") or 1.4 U/kg/day ("increased dosage"). The study had a 1-mo run-in period followed by two treatment periods each of 3-mo duration. Improvement in control occurred during "increased" insulin dosage with reduction of glycosylated hemoglobin levels (P less than 0.001), self-monitored blood glucose levels (P less than 0.001), and 24-h urine glucose excretion (P less than 0.01). Overnight studies did not reveal hypoglycemia (blood glucose less than 2 mmol/L) in either group, but improved overnight glucose profiles were demonstrated on the "increased" dosage and were associated with higher free insulin levels. The study supports the case for a higher maximal insulin dosage than commonly recommended during adolescence.