Aseptic non traumatic osteonecrosis (ON) is a painful disorder of the hip which often leads, in its final stage, to femoral head collapse and subsequent total hip replacement. Core decompression of the hip is the most widespread procedure used to treat early stage ON of the femoral head. Notwithstanding the fact that this procedure has been employed for more than three decades (2), its efficacy remains controversial (3;4). Recently, one suggested that ON might be a disease of bone cells and/or of mesenchymal cells. The levels of activity and the number of mesenchymal stem cells in both the hematopoietic and in the stromal compartments of the bone marrow have been shown to be depressed in patients with ON of the femoral head (9). The investigators have showed previously that the capacity of osteoblastic cells to replicate was decreased in the proximal femur of patients with ON of the femoral head (10). This finding raised the possibility that bone marrow containing stromal cells which have many of the characteristics of stem cell for mesenchymal tissues including bone could be implanted into the necrotic lesion of the femoral head.