From October 1983 to October 1986, 39 patients with chronic osteomyelitis (of at least two month's duration) were treated with either pefloxacin (n = 15), ofloxacin (n = 17), or ciprofloxacin (n = 7). The length of treatment ranged from 3 to 6 months; follow-up examinations were performed up until July 1988. The infecting bacterial strains (19 Staphylococcus aureus, 2 Staphylococcus epidermidis, 10 Escherichia coli, 8 Pseudomonas aeruginosa) were all sensitive to the quinolone prescribed. Twenty-nine of the 38 evaluable patients had a satisfactory outcome at follow-up examinations 14 to 48 months after the end of treatment. Fourteen of the 21 patients with gram-positive bacterial infections responded satisfactorily, as did 15 of the 17 patients infected by gram-negative bacteria. Nine cases of failure were observed (2 for pefloxacin, 4 for ofloxacin, 3 for ciprofloxacin). The infecting bacteria were Staphylococcus aureus in six cases (3 on ofloxacin, 3 on ciprofloxacin). The infecting bacteria were Staphylococcus aureus in six cases (3 on ofloxacin, 3 on ciprofloxacin), and Staphylococcus epidermidis (ofloxacin), Escherichia coli (pefloxacin), and Pseudomonas aeruginosa (pefloxacin) in one case each. In all these cases, local conditions (presence of a foreign body in 5 cases, sequestra in 3, and post-radiotherapy necrosis in 1) could have been responsible for treatment failure. Tolerance was good; adverse effects observed in the pefloxacin and ofloxacin groups disappeared after treatment was ended. Bone levels varied but were always superior to the MIC for the pathogen. In view of the satisfactory results, the possibility of oral administration, and the good tolerance, these quinolones should be considered as alternative agents for the treatment of chronic osteomyelitis.