This study was performed to assess possible delayed after-effects of acute hypoglycaemia on blood pressure (BP) and heart rate (HR) over a 24-h period. Eleven insulin-dependent diabetic patients and 11 sex, age, and body mass index matched non-diabetic subjects were studied. Blood pressure was measured using a non-invasive ambulatory blood pressure monitor following acutely induced hypoglycaemia in the morning. No significant differences were observed in 24-h systolic and diastolic BP and HR in either groups, between the day when hypoglycaemia was induced and the day when plasma glucose was kept normal. In diabetic patients, hypoglycaemia induced a temporary but significant fall in mean BP (-7 +/- 1 mmHg vs -2 +/- 2; p < 0.05). Plasma glucose levels were significantly higher in insulin-dependent diabetic patients following hypoglycaemia than in those observed during the reference test. This study demonstrates that acute hypoglycaemia in insulin-dependent diabetic subjects does not cause significant alterations in 24-h BP in either diabetic or normal subjects.