Calcium-phosphor metabolism was studied in patients with active acromegaly with or without osteoporosis, mean age 45.2 +/- 11.4 years and mean duration of the basic disease 5.52 +/- 3.6 years. No significant deviations and no direct relation with the high serum growth hormone and prolactin levels were found. The normal basic secretion of the calcitrophic hormones--parathyroid hormone and calcitonin and their normal response to the hypercalcemia after intravenous calcium load of the patients with and without osteoporosis reject their direct participation in the pathogenesis of osteopenia. The changed skeletal sensitivity to calcitrophic hormones closely connected with the patients' age and the duration of the basic disease in combination with many other factors probably plays a major role in the pathogenesis of osteopenia.