Rifampicin levels in serum, cortical bone and spongious bone were measured by a biological assay in 13 non-infected patients undergoing total replacement of the hip. Samples were collected after 24-72 hours rifampicin administration (daily oral dose: 600 mg). The mean level was 0.67 +/- 0.48 microgram/g in cortical bone and 3.35 +/- 0.72 microgram/g in spongious bone. Rifampicin diffusion was also assessed in normal bone from crista iliaca needle biopsy specimens in 7 patients treated for osteitis or septic arthritis. Bone and serum levels did not appear linearly correlated but, in any case, bone levels were much higher than MIC for Staphylococcus aureus which is usually involved in bone and joint infections.