Thirteen patients with bone infection caused by Staphylococcus aureus, Pseudomonas aeruginosa, Serratia marcescens or Escherichia coli in association with implanted foreign material were treated with pefloxacin 400 mg 12-hourly for up to six months. Satisfactory results, with fistula closure and eradication of the infecting bacteria, were achieved in nine patients, who have been followed up for four to seven years. Treatment failed in two patients, with re-isolation of the infecting bacteria (P. aeruginosa; Ser. marcescens) which showed reduced sensitivity to pefloxacin. Primary failure (failure to close of the fistula and re-isolation of bacteria sensitive to pefloxacin) occurred in one patient, who achieved a satisfactory result later after removal of foreign material. Relapse after treatment occurred in one patient. Eight patients suffered migrating arthralgia (without signs of arthritis) but this did not interfere with the treatment, which was generally well tolerated.