Calcium and phosphate metabolism has been studied in eight patients with active acromegaly. Plasma calcium, phosphate, alkaline phosphatase, creatinine and parathyroid hormone levels were in the normal range in all patients, while urinary calcium excretion, calcium/creatinine ratio and hydroxyproline were higher than in controls (p less than 0.01, p less than 0.01, p less than 0.02, respectively). Basal plasma calcitonin levels were in the normal range and stimulation with calcium (3 mg/kg body weight in 10 min) showed similar calcitonin responses in acromegalic and normal subjects. Our data show that in normocalcemic acromegaly with high bone turnover calcitonin secretion is not abnormal.