The objective of this study was to compare glycemic thresholds for hypoglycemic responses in obese and control subjects. A modified glucose-clamp technique was used to produce a standardized fall in plasma glucose (0.5 mmol/l per 40 min) in nine morbidly obese and ten control subjects. The release of the counter-regulatory hormones was measured and a symptom questionnaire was filled out every 10 min. The hypoglycemic thresholds (taken as the plasma glucose level where the response exceeded the basal level +2 s.d.) were practically identical in the two groups both for the hormones and the symptoms (including hunger). Our results argue against the hypothesis that an increased sensitivity to a falling plasma glucose is of importance in the pathogenesis of obesity.