The in vivo biocompatibility of metals coated with several different types of ceramics [alumina (alpha-Al2O3), titanium oxide (TiO2), titanium nitride (TiN), and hydroxyapatite (HAP)] was investigated. These composites had been devised for the purpose of incorporation into the stem of a total hip prosthesis. The materials were inserted into the mid-diaphyseal region of the femurs of adult dogs, and follow-up quantitative histological comparisons were performed for a period of up to 96 weeks. HAP-coated composites showed the best biocompatibility.