The glycaemic and hormonal responses to a hypoglycaemic event induced by an i.v. bolus of insulin was studied in seven type 1 diabetic patients treated first with continuous subcutaneous insulin infusion (CSII) and subsequently with continuous intraperitoneal insulin infusion (CIPII). Arterialised blood glucose and venous hormonal responses were analyzed. HbA1c was improved by CIPII. Although a regimen of a higher basal insulin infusion rate was applied during CIPII the basal peripheral venous insulin levels were lower. The i.v. bolus of insulin resulted in hypoglycaemia in both tests but was more pronounced during the CSII test expressed as a smaller area under the curve (AUC) for the first hour (13.0 +/- 2.3 vs. 13.7 +/- 1.2 mmol l(-1) h(-1), p=0.016, CSII vs. CIPII). The hypoglycaemia resulted in a significant and similar increase in the plasma levels of adrenaline, cortisol and growth hormone in both experiments. A significant increase in the glucagon level was only observed during CIPII. The incremental glucagon response was also significantly more pronounced in the CIPII test expressed as maximal responses (7.5 +/- 3.0 vs. 17.0 +/- 3.1 pg ml(-1), p =0.048, CSII vs. CIPII) as well as incremental AUC (5.1 +/- 12.0 vs. 44.4 +/- 13.2 pg ml(-1) h(-1), p =0.027, CSII vs. CIPII). It seems that CIPII in type 1 diabetic patients could improve the glucagon release to hypoglycaemia. This observation may contribute in explaining why CIPII is associated with a lower incidence of hypoglycaemia in spite of an improvement in metabolic control.