The effect of intensified metabolic control obtained with continuous subcutaneous insulin infusion (CSII) on the frequency and symptoms of hypoglycaemia was studied in type I diabetic patients. The reproducibility of the questionnaire used to evaluate the hypoglycaemic symptoms was verified in a control group receiving unchanged conventional insulin therapy for 2 months. Metabolic control was significantly improved during CSII (HbA1c 6.8 +/- 0.4% versus 8.7 +/- 0.7%, normal range up to 5.4%) in all patients while no change was seen in the control group. The results of frequent self glucose monitoring showed that the incidence of low glucose levels (below 3.5 mmol/l) increased about threefold in the CSII group. Awareness of hypoglycaemia was clearly changed during CSII with less pronounced adrenergic symptoms while no alterations were found in the group with unchanged metabolic control. These results emphasize the importance of regular self glucose monitoring during CSII and of informing the patients that their hypoglycaemic symptoms may change during intensified control.