Three out of 140 patients with non-hodgkin's lymphoma treated in a Department of Internal Medicine showed hypercalcemia during their clinical course. Hypercalcemia was symptomatic in two patients causing renal failure in one of them and a metabolic encephalopathy in the other. In the third case hypercalcemia was a casual finding. Serum calcium levels varied between 14.8 and 16.6 mg/100 ml; serum phosphate and tubular reabsorption of phosphate were normal. Alkaline phosphatase were high in the three cases. Bone disease was present in two cases. Transient responses were obtained with the administration of prednisone and calcitonin associated to forced diuresis. Indomethacin was ineffective. Pathogenesis of hypercalcemia could be related to the release of an osteoclastic activator factor. The role of prostaglandins and the presence of PTH-like mechanisms were discarded in our cases by indirect methods. The poor prognosis of patients with non-hogkin's lymphoma and hypercalcemia in stressed.