Cushing's syndrome where, we believe, an excess of the adrenal cortical" sugar" or" S" hormone inhibits anabolism of protoplasm including bone matrix (2, 6);(5) adaptation syndrome of Selye (7), where, we believe, the pathological physi-ology is the same asin Cushing'ssyndrome;(6) idiopathic osteoporosis, where the cause of the condition remains obscure;(7) acromegaly, where the cause may be the increase of pituitary hormone (s), or thesecondary lack of gonadal hormones (8); and (8) the post-menopausal state, the commonest of all forms, where the difficulty is a deficiency in estrogen to stimulate the osteoblasts. Frequently 2 or more factors com-bine inone individual; thus, after an orthopedic operation (see Cases 7, 8, and 9, below) factors (1) and (5) probably both play a part.