Heparin has been used since 1936 for the treatment of vascular thrombotic episodes, but the association between heparin administration and osteopenia in man was not reported until 1964, when a causual notation was made regarding a spontaneous vertebral fracture in a 50-year-old man on heparin with no history of trauma (10). Jaffe and Willis (24) later reported the development of multiple symmetrical rib fractures, compression fractures of the thoracic vertebrae, and generalized skeletal demineralization in a 41-year-old man subjected to heparin at 20,000 units/day for 1 year. Earlier in the same year, Griffith et al. (18), reporting on 117 patients subjected to long-term heparin therapy, noted that 10 patients on subcutaneous heparin at 15,000 – 30,000 units/day for 6 months or longer developed spontaneous vertebral and/or rib fractures. These complications were not observed, however, in 107 patients receiving 10,000 units/day or less for 1 – 15 years. Bone biopsies obtained from two patients with osteopenia revealed that “the bony matrix was very soft, offering little or no resistance to the pathologist’s knife” (18).