The results of the treatment of twenty-one patients (age 22-66 years) with chronic bone or joint infections with ciprofloxacin were evaluated. The osteomyelitis was secondary to trauma in 12 patients, joint replacement in six, previous acute hematogenous infection in two and osteotomy in one. Stafylococcus aureus (11 times) and Pseudomonas aeruginosa (9 times) were most frequently cultured. The duration of ciprofloxacin therapy averaged 76 days. Concomitant antimicrobial drugs were used in one patient only. Fifteen patients were operated during treatment; in most cases the surgical procedure consisted of a thorough debridement. Nineteen patients could be evaluated. The bacteriological results were as follows: eradication 27; marked reduction 1; eradication with recurrence 1. Contamination occurred in five patients and superinfection in two, without much influence on the final outcome. The investigator's assessment at the end of the therapy was as follows: complete success in 14 patients and partial success in seven. During the follow-up (3-13 months) the therapy was judged completely successful in 16, partially successful in four and unsuccessful in one. Two patients had minor gastric complaints during therapy and one showed a temporary slight increase in the liver transaminases.