The metabolic and hormonal responses to oral glucose were studied in a patient with a pheochromocytoma before treatment, after alpha-blockade, after combined alpha- and beta-blockade, and after surgical removal of the tumor. Before treatment, fasting blood glucose was elevated [6.5 mmol/liter (117 mg/dl); normal range, 4.2--5.5 mmol/liter (75--100 mg/dl)], as was the fasting plasma nonesterified fatty acid level (1.19 mmol/liter; normal range, 0.06--0.7 mmol/liter), the blood total ketone body concentration (0.50 mmol/liter; normal range, 0.02--0.44 mmol/liter) and the lactate ot pyruvate ratio (16.2; normal range, 5.9--15.01. These abnormalities were corrected by alpha-adrenergic blockade alone and together with beta-blockade. Oral glucose tolerance (50 g) was mildly impaired in the untreated state, and the insulin response was decreased. Both alpha- and alpha- plus beta-blockade restored the insulin response to glucose but failed to correct the glucose intolerance. Three months after removal of the tumor, all metabolic findings were normal. The correction of the fasting metabolite concentrations and serum insulin levels by alpha-adrenergic blockade suggests that an alpha-adenergic effect causes the original metabolic abnormalities. The residual glucose intolerance after adrenergic blockade may result from incomplete blockade or factors other than alpha- and beta-adrenergic activity.