28 patients with osteoarthritis or avascular necrosis were included in a study examining the level of metal particles in the serum after total hip replacement (THR) using alternative bearing surfaces. Patients were randomized to receive THR with ceramic-on-ceramic or metal-on-metal couplings. At 1 year post-operation, the serum aluminium level of patients in either group did not differ significantly from their pre-operative levels. There was also no significant change in the cobalt level of the ceramic-on-ceramic patients; however, the metal-on-metal patients demonstrated a significant increase in their cobalt level after 1 year.