Suspected postprandial (reactive or idiopathic) hypoglycemia is characterized by predominantly adrenergic symptoms appearing after meals rich in carbohydrates and by their rare association with low blood glucose level (< 2.77 mmol/L). We studied heart rate, blood pressure, plasma insulin, C-peptide, and catecholamine responses during a 5-h oral glucose tolerance test in eight patients with suspected postprandial hypoglycemia and eight age-, sex-, and body mass index-matched healthy controls. We also evaluated beta-adrenergic sensitivity by using the isoproterenol sensitivity test. Psychological profile was assessed by the Symptom Checklist (SCL-90R) self-report symptom inventory. Patients with suspected postprandial hypoglycemia had higher beta-adrenergic sensitivity (defined as the dose of isoproterenol required to increase the resting heart rate by 25 beats/min) than controls (mean +/- SEM, 0.8 +/- 0.13 vs. 1.86 +/- 0.25 microgram isoproterenol; P = 0.002). After administration of glucose (75 g) blood glucose, plasma C-peptide, plasma epinephrine, and plasma norepinephrine responses were identical in the two groups, but plasma insulin was higher in the patients (group effect, P = 0.02; group by time interaction, P = 0.0001). Both heart rate and systolic blood pressure were significantly higher (but remained in the normal range) after glucose administration in patients with suspected postprandial hypoglycemia than in controls (group by time interactions, P = 0.004 and 0.0007, respectively). After glucose intake, seven patients had symptoms (palpitations, headache, tremor, generalized sweating, hunger, dizziness, sweating of the palms, flush, nausea, and fatigue), whereas in the control group, one subject reported flush and another palpitations, tremor, and hunger. Analysis of the SCL-90R questionnaire revealed that patients had emotional distress and significantly higher anxiety, somatization, depression, and obsessive-compulsive scores than controls. We may conclude that patients with suspected postprandial hypoglycemia have normal glucose tolerance, increased beta-adrenergic sensitivity, and emotional distress.