Biopsy specimens of cartilage and subchondral bone were obtained from the weight-bearing dome of the acetabulum in twelve elderly patients who were having a revision of a hemiarthroplasty of the hip because of pain. Biopsy specimens of acetabular cartilage and subchondral bone were also obtained from eight patients of comparable age who were having a primary hemiarthroplasty for a displaced fracture of the femoral neck; these served as the control specimens. The specimens were stained with hematoxylin and eosin for the initial histological assessment of cartilage structure and cellularity as well as the integrity of the tidemark. Safranin-O and toluidine-blue stains were used to assess proteoglycan content. A histological grading scale was employed for comparative analysis of samples. The joint space of the hip was measured on the radiographs that were made before the revision and was correlated with the histological grade. Review of the histological specimens demonstrated considerable degeneration of acetabular cartilage in the patients who were having a revision of a hemiarthroplasty as compared with that in the age-matched control patients who were having a primary hemiarthroplasty. The progression in the severity of the degeneration correlated directly with the duration of articulation of the implant with the acetabulum. All six of the patients in whom the implant had been in situ for more than five years, and in whom the femoral stem was determined to be stable at the operation, had nearly complete loss of cartilage as seen on histological examination.(ABSTRACT TRUNCATED AT 250 WORDS)