The autors have taken the measurement of bone marrow pressure of the femoral head in the 115 hips of 79 patients with osteonecrosis of the femoral head and in the 8 hips of 5 patients with osteoarthritis of the hip joint from February, 1989 to May, 1991, and have analyzed the difference of bone marrow pressure between the subchondral area and neck. 1. According to the causes, base-line pressure in the neck was higher than one in the subchondral area, except in caisson disease, but provocative pressure in the subchondral area was higher than one in the neck, except in post-traumatic avascular necrosis. 2. Accodring to the Enneking stage, base-line pressure in the neck was higher than one in the subchondral area except in stage VI, but provocative pressure area was higher in the subchondral area. 3. According to radiologic types, base-line pressure in the neck was higher than one in the subchondral area, but provocative pressure in the subchondral area was higher than one in the neck. 4. In osteoarthritis, both of base-line pressure and provocative pressure in the subchondral area were higher than one in the neck. 5. There is no significant difference of bone marrow pressure between the subchondral area and the neck area according to causes, stage and radiologic pattern (p>0.05). 6. Because all cases showed increased pressure in both of the subchondral area and neck, it was sufficient to diagnose the osteonecrosis of the femoral head by measuring bone marrow pressure only in the neck area; periphery of the necrotic center. 7. In the osteonecrosis of femoral head, increased bone marrow pressure seems not to be a cause of the disease process but a result of it. And the measurement of bone marrow pressure is not a specific diagnostic value but a sensitive one. 8. The necrotic center is a dead space due to interruption of systemic circulation, and has a poor functional capacity as pressure absorber.