Interruption of a continuous subcutaneous insulin infusion, most often due to technical problems occurring during the night, is a not uncommon event whose metabolic consequences have received relatively little attention until now. We have therefore investigated the changes in blood glucose, plasma non-esterified fatty acids, 3-hydroxybutyrate, glucagon and free insulin in eight C-peptide negative Type 1 diabetic patients whose pumps were deliberately stopped between 23.00 h and 05.00 h. A control test with the pump functioning normally was carried out in each patient and the studies were randomized. Considering the values at 23.00 h as reference, interruption of the insulin infusion resulted in (1) a rapid decrease in plasma free insulin significant after 1 h and reaching a nadir of 6 +/- 2 mU/l after 6 h; (2) a rise in blood glucose which was significant at hour 3 and reached 17.4 +/- 1.9 mmol/l at hour 6; (3) a moderate increase in plasma nonesterified fatty acids which remained in the range of 700-800 mumol/l; (4) an early and linear rise in plasma 3-hydroxybutyrate, significant after 1 h and averaging 1290 +/- 140 mumol/l after 6 h; (5) a late increase (hour 5) in plasma glucagon. The second aim of our study was to provide for the patient a precise scheme of insulin supplements administered via the pump and based on blood glucose monitoring (Dextrostix - Glucometer) and semi-quantitative evaluation of ketonuria (Acetest). Resetting the pump at its basal rate at 05.00 h and giving insulin supplements (2-8 U) at 06.45 h (with the usual breakfast dose) and again at 10.00 h have proved efficacious in restoring satisfactory metabolic control by noon the day after starting the experiment. These results form practical recommendations to patients undergoing this type of accident.