The therapeutic effectiveness of adjuvant therapy with fosfomycin was studied in a prospective clinical trial of 60 patients suffering from chronic post-traumatic osteomyelitis. The patients were aged between 17 and 78 years (mean 37.4 years). The chronic osteomyelitis was predominantly located in the tibia (43 patients) and in the femur (13 patients). Most of the pathogens isolated were Staphylococcus aureus (42%), coagulase-negative staphylococci (19%), Pseudomonas aeruginosa (12%), streptococci (7%) and enterococci (5%). The pathogens isolated from the osteomyelitic foci were sensitive to fosfomycin. Fosfomycin concentrations in bone samples were determined in 19 patients. In the group of patients receiving initially 5 g fosfomycin, bone concentrations ranged between 119.4 and 451.2 mg/l of interstitial fluid. In the group of patients receiving initially 10 g fosfomycin, bone concentrations ranged between 117.1 and 3684.2 mg/l of interstitial fluid. The mean MIC90 values of the isolated pathogens ranged between 2 and 64 mg/l (S. aureus and Escherichia coli 2 mg/l, Proteus vulgaris 8 mg/l, streptococci groups A and B 32 mg/l and coagulase-negative staphylococci, enterococci and P. aeruginosa 64 mg/l). The outcome of treatment was assessed after a minimum of seven and a maximum of 53 months (mean 37 months). The results were: very good 54.7%, good 3.8%, satisfactory 15.1% and unsatisfactory 26.4%.