For successful treatment of bacterial osteomyelitis the administered antibiotic must reach sufficiently high concentrations in bone tissues. Therefore concentrations of enoxacin in bone in ten patients requiring hip surgery were measured. To prevent a postoperative infection, 400 mg enoxacin b.i.d. for two days were administered. On an average 120 (90-210) min after the final dose samples of venous blood and bone tissue were taken. The bone pieces were divided into corticalis and spongiosa. Using a bio-assay-method the following concentrations were found: (mean +/- S.D.): serum 2.88 ( +/- 0.90) mg/l, corticalis 5.90 ( +/- 0.79) mg/kg, spongiosa 3.95 ( +/- 1.01) mg/kg. Thus enoxacin reaches higher levels in bone tissue than in serum.