Remission of diabetes was attempted in 12 recent acute onset ketosis-prone juvenile diabetes after short term (5 +/- 1 days) but excellent blood glucose control by the external artificial beta-cell. The comparison group comrised patients undergoing traditional treatment (n = 28). Nine (75%) persistent (over 3-14 months of duration) although partial (oral drugs required) remissions were obtained in the former group as compared to 3 (11%) in the latter group (p less than 0.05). Cases which showed remissions after insulin infusion had a plasma insulin response to IV glucagon still present before insulin infusion, and a daily urinary C-peptide excretion significantly enhanced after (p less than 0.01). Urinary C-peptide/blood glucose remained improved during the remission period. Thus, early effective treatment by means of the artificial pancreas may break the vicious circle hyperglycaemia-insulin depletion-hyperglycaemia and lead to frequent and sustained remissions of juvenile diabetes.