An increase of marrow mast cells together with plasma cells and lymphocytes has been observed in a variety of conditions: inflammations, wound and fracture healing, oedema and fibrosis (Fig. 76.1). Immunocytic and lymphocytic marrow infiltrations often have a high content of mast cells. Certain tumours may contain numerous mast cells. Mast cell proliferation as osseous surfaces is also a consequence of primary and secondary HPT. There is also a relation between mast cells and postmenopausal osteoporosis, suggesting that mast cells accelerate trabecular bone loss.