The pharmacokinetics of the novel, rapid-acting insulin aspart were compared with those of soluble human insulin following subcutaneous administration in nine children (aged 6–12 years) and nine adolescents (aged 13–17 years) with stable type 1 diabetes. The study had a randomised, double-blind, two-period crossover design. Each patient received a single subcutaneous dose of insulin aspart or human insulin (0.15 IU/kg body weight) 5 min before breakfast and the plasma insulin and glucose concentrations were measured at intervals during the following 5 h. The pharmacokinetic profile of insulin aspart differed significantly from that of human insulin with a higher mean maximum serum insulin (C_{max ins}), 881 ± 321 (SD) pmol/l versus 422 ± 193 pmol/l for human insulin (P < 0.001); and with a shorter median serum insulin t _{max ins}, 40.0 min (interquartile range: 40–50 min) versus 75.0 min (interquartile range: 60–120 min) for human insulin, (P < 0.001). An age-related effect on C_{max ins} and area under the curve (AUC_{0–5h ins}) was observed with higher values in adolescents than in children for both insulin aspart and human insulin. Postprandial glycaemic control was improved with insulin aspart; the baseline-adjusted ΔC_{max glu} being lower for insulin aspart compared with human insulin (increase of 7.6 ± 5.1 versus 9.4 ± 4.4 mmol/l respectively, P < 0.05). The incidence of adverse events was similar for the two insulin types.