40 patients with chronic osteomyelitis were treated per os with the bactericidal beta-lactam-antibiotic cephalexin during 3 to 60 weeks. In 16 patients, who were operated simultaneously, bacterial spreading was prevented by a combination of cephalexin and parenteral cephaloridin during operation and in the postoperative period. In these patients no recurrence occurred during the follow up time (2 to 5 years). In 34 patients general and local signs of inflammation diminished under cephalexin therapy and a complaint-free interval of at least 6 months followed. No serious side effects forcing a stop of therapy were observed. According to the gained experiences oral cephalexin in combination with perenteral cephaloridin is indicated for prevention of bacterial spreading during operations in chronic bone infections and in patients with acute febrile recurrence of chronic osteomyelitis refusing a surgical intervention.