A 10-year follow-up study was made on a consecutive series of 93 patients who underwent hip replacement with a metal-to-metal prosthesis - Müller's so-called self-lubricating total hip prosthesis - during the years 1967-1970. Primarily 106 hips were operated on. One-third of the patients died within the 10-year period. Of the other two-thirds (63 patients/75 primarily operated hip joints), 38 (57 per cent) still had their primary prostheses and 29 had undergone reoperation. In 18 of the reoperations a new prosthesis was inserted and in 11 the extraction of the primary prosthesis was not followed by replacement. All 63 surviving patients could be traced at the 10-year follow-up. The majority attended for personal examination, including evaluation of pain, walking ability and range of hip movement, and for radiography. In the group who had retained their primary prosthesis there was on the whole a rather good hip function - nevertheless in 75 per cent of these patients signs of loosening of the prosthesis were visible radiographically. Of the patients who had undergone reoperation, those with an exchange prosthesis had a better functional capacity than those who were left with a so-called Girdlestone-hip. Deep infection occurred in 8 per cent of the primary 106 cases. There was no onset of infection later than 4 years after the primary surgery.