The biochemical parameters of calcium metabolism were measured in patients suffering from bone metastases of prostatic origin. In 14 patients with sclerotic bone lesions, serum calcium and serum phosphorus were significantly lower than in controls. Serum alkaline phosphatase levels, which reflect osteoclastic bone formation, and urinary hydroxyproline, which reflects osteoclastic bone resorption, were both increased. 25-Hydroxyvitamin D (25-OHD) levels were appropriate for the age of the patients but serum immunoreactive parathyroid hormone (iPTH) and 1,25-Dihydroxyvitamin D (1,25-(OH)2D) levels were significantly increased. In contrast, no significant changes wee noted in 3 patients with pure osteolytic lesions. We conclude that the patients with sclerotic bone metastases have a high bone formation which frequently induces a secondary hyperparathyroidism and increased 1,25-(OH) 2D levels. A calcium and/or vitamin D supplement could therefore be advantageous in patients having symptomatic hypocalcemia or osteomalacia.