In normal subjects there is a positive linear correlation between the osteoid volume and the surface of trabecular bone covered with osteoblasts (Merz and Schenk, 1970b). In intestinal malabsorption and in nutritional vitamin D deficiency, this is no longer true: the osteoid volume can be raised and the number of osteoblasts inadequate, suggesting a defect in mineralization. With the addition of vitamin D the osteoid volume is normalized and the number of osteoblasts approbiate, suggesting normal mineralization. Osteoclastic bone resorption is increased in intestinal malabsorption and in nutritional vitamin D deficiency, irrespective of the serum calcium concentration and particularly in normocalcaemic patients. Bone resorption and new bone formation are coupled, as evidenced by a positive linear correlation, between the trabecular surface covered with osteoclasts and with osteoblasts. Possible effects of parathyroid hormone and/or vitamin D on bone remodelling are discussed.