In a double-blind study comprising 36 patients the effect of a three-month course of ciprofloxacin on chronic reactive arthritis was evaluated. At the end of the follow-up period 6 months after stopping the therapy, arthralgia, pain at movement and morning stiffness had decreased significantly compared to the values before the treatment in the ciprofloxacin group, whereas the Ritchie index and ESR showed a significant decrease in the control group. We conclude that further studies are necessary before the value of prolonged ciprofloxacin treatment of chronic reactive arthritis can be established.