Crystal distribution in articular cartilage of femoral heads resected at hip arthroplasty for fracture of the femoral neck was examined in 10 patients (77-91 years) by computerised image analysis of electron micrographs. Crystal content of the zenith did not differ from that of the infrafoveal region of the femoral head in the superficial 0.5 mm of the cartilage. Crystal area density (percentage area of the section occupied by crystal profiles) was higher in a zone 0-50 microns than in the subjacent zone 50-500 microns from the articular surface, particularly in the zenith of the femoral head. It was also higher on the superficial (towards the articular surface) aspect than on the deep aspect of cells in perilacunar matrix. Crystal area density was similar in lacunar matrix, perilacunar matrix, and matrix remote from cells. Matrix containing cell debris was more heavily impregnated with crystals than any other site. No difference in crystal content was observed in cartilage beneath articular surfaces which were ultrastructurally smooth or roughened. The diminishing gradient of crystal area density with depth from the articular surface, the absence of a marked spatial association with living cells, and the impregnation of sites containing cell debris suggest that crystal deposition in these cases is not due primarily to chondrocyte activity.