To determine whether remodelling of subchondral bone in osteoarthritis is related to anatomical and mechanical factors operating on the joint surface. Ten femoral heads were examined. Patients due to have the femoral head removed because of osteoarthritis were given a double tetracycline label before surgery. The specimens were divided in three roughly equal parts, corresponding to the medial, central (weight bearing), and lateral aspects of the femoral heads. Undecalcified methylmethacrylate embedded sections were prepared. The subchondral bone was assessed for appositional bone formation by ultraviolet light microscopy, for resorptive activity by osteoclast count, and for trabecular bone volume by semiautomatic computerised image analysis. Appositional bone rate was also correlated with the presence or absence of overlying cartilage. Bone density was reduced in the medial aspect of the femoral heads but there was no significant difference between the appositional bone rate or the resorptive activity in the three areas. Nor was there any correlation between appositional bone rate in the subchondral bone and the presence or absence of overlying cartilage. Remodelling of subchondral bone in osteoarthritis, at least in the short term, is fairly constant and is not related to weight bearing.