Osteonecrosis of the jaw is a particular form of chronic osteomyelitis caused by bisphosphonates (BF) or by other pharmacological or anti-angiogenic drugs. The BF are potent drugs inhibitors of osteoclasts by exerting a strong interaction with these cells, producing a sharp decrease of bone resorption. Objectives: To analyse clinical and radiologic characteristics as well as differences in the plasma levels of the Activation Nuclear Kappa receptor ligand (RANKL) and of osteoprotegerin (OPG) in a group of patients with osteonecrosis and compared to healthy controls. In addition, within the Group of patients with osteonecrosis maxillary study if there is relationship between plasma levels of OPG and RANKL and clinical data. Material and methods: a clinical study in 183 cases of Osteonecrosis of the jaw by bisphosphonates intravenous and oral bisphosphonates in patients with osteoporosis and oncologic patients. Analyze a study x-ray in three groups: Group 1 consisting of 30 cases selected from the 183 of the clinical study, group 2 comprised 30 patients without pathology in the jaws and group 3, 30 cases of Group 1, but of the healthy contralateral areas. Finally, the determination of plasma levels using an assay enzyme-linked immunosorbent enzymes or ELISA, to measure the plasma levels of OPG and RANKL in three groups of patients