After onset of type I diabetes 7 diabetics were randomized to subcutaneous insulin pump treatment (CSII) (age 12 to 29 years, mean: 21 years) and 7 diabetics to conventional insulin treatment (CI) (age 14 to 28 years, mean: 21 years). HbA1, glycosylated serum proteins and mean blood glucose (MBG) as parameters of metabolic control were determined monthly. After 2 months both groups showed HbA1 values in the normal range. Mean MBG values were (mean +/- SD) 116 +/- 7 mg/dl for CSII and 118 +/- 14 mg/dl for CI. Residual insulin secretion was determined monthly by fasting C-peptide. After 14 days, 5, 7, 8 months fasting C-peptide values were significantly (P less than 0.05) higher in CI. After one year fasting C-peptide was comparable in both groups (CSII and CI mean: 0.06 nmol/l). The administered insulin dose was comparable in both groups with a 55% reduction of insulin dose after 5 months in CSII (0.35 +/- 0.15 U/kg/24 h) and in CI after 7 months (0.31 +/- 0.28 U/kg/24 h). After 12 months of insulin therapy about 60% of the initial insulin dose was injected in both groups. 1 patient on CSII (12 years) and 2 patients on CI (15, 28 years) showed a complete remission (for 3-9 months) with no exogenous insulin and normal HbA1 values. 50% of the patients had episodes where they did need less than 0.2 U/kg/24 h insulin to maintain optimal diabetic control (3 CSII, 4 CI). During the first year of insulin treatment in type I diabetes with CSII as well as with CI a comparable near normalisation of diabetic control could be achieved.