Review of publications in which the pharmacokinetics of ofloxacin and ciprofloxacin were compared directly indicates that although similar in many respects, these fluoroquinolones exhibit three differences that may be important clinically. First, ofloxacin is more completely absorbed, achieves higher peak serum concentrations, and has a longer terminal elimination half-life, which result in a fivefold greater area under the curve than that of ciprofloxacin when similar doses are orally administered. Ofloxacin's more favorable pharmacokinetic profile seems to compensate at least in part for the greater activity of ciprofloxacin against gram-negative bacilli in vitro. Second, ofloxacin is eliminated almost entirely via the kidneys, whereas ciprofloxacin is eliminated via both the kidneys and non-renal routes. This suggests that ciprofloxacin may be preferable for patients with variable renal function, whereas ofloxacin may be preferable for patients receiving dialysis because of the need for less frequent administration. Third, concomitant use of ciprofloxacin with either theophylline or caffeine decreases elimination and thereby results in elevated serum concentrations of these methylxanthine derivatives. Because ofloxacin does not cause clinically significant alterations in the pharmacokinetics of either theophylline or caffeine, it may be preferable for patients using these concomitantly.