We compared radiologically two groups of total hip prostheses, 36 porous-coated and 51 hydroxyapatite-coated, which had been implanted in 87 hips of 73 patients with avascular necrosis of the femoral head. Radiographs were taken at postoperative 1 year and 2 year, and used to compare various radiological parameters between the two groups. For the acetabular side radioluscent line and osteolysis were evaluated, and for the femoral side radioluscent line, osteolysis, stress shielding. endosteal new bone formation, subsidence and cortical hypertrophy were evaluated; their location was identified according to the zones described by DeLee and Charnley for the acetabulum and according to those described by Gruen et al for the femur. In both groups there was no subsidence. In terms of osteolysis, stress shielding and cortical hyper-trophy there was no significant difference between the two groups throughout the period. Radioluscent line in the acetabulum was more common around the porous-coated cup, but was focal and not progressive. The rate of radioluscent line in the femur was a little higher around hydroxyapatite-coated stem especially in zone 5. Endosteal new bone formation was excellent in both groups, but was more extensive around hydroxyapatite-coated stem. This study suggests that hydroxyapatite coating play a certain role in terms of bony ingrowth.