A study was made of a McKee-Farrar total hip prosthesis which had been removed because of aseptic loosening after nearly four years in the body. The wear areas of the metallic surfaces were mapped. From microscopic studies, three types of wear were determined: Type-1 wear was an initial surface scratching; type-2 wear was when a new smooth surface had formed; and type-3 wear was a pitting on the type-2 wear surface. The depth of wear was estimated by stylus profilometry to be only about one micrometer. The volumetric wear was calculated to be much less than is encountered, on average, for metal-on-plastic total hip joint prostheses. Further studies were carried out on several other specimens of removed McKee-Farrar prostheses to verify and clarify the previous findings.