Since the introduction of biologic fixation to solve the problem of late aseptic loosening af1er cemented total hip arthroplasty, osteolyses around the stably fixed components have been reported with increasing frequency, which is thought to be caused mainly by polyethylene particles shedded from the liner of acetabular component. From Dec. 1987 to Feb. 1993, 73 cementless total hip arthroplasties were performed by one surgeon and 50 cases were followed for more than 2 years (mean 3 years 8 months), among which four cases of localized osteolysis were found around the stable acetabular components(incidence:8%) and the details are as follows: 1. There were three male and one female patients, with the mean age of 38 years. 2. The mean duration after operation was 4 years 3 months. 3. The acetabular cups and stems in all cases were stably fixed by radiological criteria. 4. The size of acetabular cup was less than 50mm in all cases. 5. The size of femoral head was 28mm in two cases and 26mm in the remaining two cases. 6. Revision of the acetabular cup was done in three cases. 7. Histological study of the curettage specimen in three revised cases showed findings suggestive of foreign body reaction and chronic inflammation, nontheless polyethylene particles were not found under polarized microscope. From the above review, it is construed that the occurrence of localized osteolysis around the acetabular components after total hip replacement is influenced by such factors as the size of head and the thickness of acetabular liner-frequent occurrence in cases with small acetabular cup and relatively large head, thus making the use thin polyethylene liner inevitable and the inner liner more prone to wear-although the authors were unable to reveal polyethylene particles in osteolytic lesions by histological study.