Simultaneous reduction in the bone formation phase, and a normal or accelerated bone resorption phase of the bone remodelling process occurs in patients with severe osteoporosis having normal calcium or mineral intake, endocrine function, and exercise patterns. A large body of research suggests that the resorption phase is under the control of the immune system, cell mediated, and involves interaction of macrophages and T-lymphocytes. Much less is known about the bone formation phase. The present hypothesis is based upon speculation on the immunosuppressive effects of B-cell-synthesized humoral antibody (anti-BMP) against bone morphogenetic protein, subsequently reducing osteoprogenitor cell differentiation and causing either gradual or precipitous decline in bone mass. The hypothesis assumes that approximately 74% of white Caucasian women of postmenopausal age, and nearly all of the black population in the USA who do not develop osteoporosis, maintain a low anti-BMP titre. The hypothesis emphasizes a recorded (albeit low) incidence of osteoporosis in children, postpartum women, young men, exogenous adrenal hypercorticoidism, various endocrinopathies who warrant investigation for auto-immune disease. Based upon a high anti-BMP titre, and a low BMP anti-BMP ratio in 10 patients with severe osteoporosis, the hypothesis proposes investigation of an auto-immune disorder in the 26% of the female population who become disabled by severe osteoporosis.