Osteomyelitis with Staphylococcus aureus was established in the tibiae of twenty-six adult mongrel dogs. After confirmation of infection at four weeks, all animals had operative debridement and were then divided into three treatment groups. Group 1 (eight animals [sixteen tibiae]) was treated with parenteral administration of gentamicin (three milligrams per kilogram of body weight per day) every eight hours for four weeks. Group 2 (nine animals [nine tibiae]) was treated with a polymethylmethacrylate implant containing 100 milligrams of gentamicin that was placed in the tibia for six weeks. Group 3 (nine animals [nine tibiae]) was treated with a polylactide/polyglycolide implant containing 100 milligrams of gentamicin that was placed in the tibia for six weeks. All animals were killed at the end of treatment. At that time, specimens of tissue were obtained for quantitative culture as well as for antibiotic immunoassay. In the groups that had been treated with an implant, serum was obtained for the measurement of serum drug levels after debridement; after the implantation; four, seven, and twenty-one days postoperatively; and immediately before the animals were killed. The infection was eradicated in ten of the sixteen tibiae in Group 1, in eight of the nine tibiae in Group 2, and in all nine tibiae in Group 3.(ABSTRACT TRUNCATED AT 250 WORDS)