We evaluated the bioavailability of ciprofloxacin at two dose sizes in eight healthy volunteers. Each volunteer was given 200 mg of ciprofloxacin both orally and intravenously in a randomized crossover fashion and 750 mg orally. Bioavailability at the two doses was similar: 69 and 69.1% for the 200- and 750-mg doses, respectively. However, the bioavailability observed with the 750-mg dose was significantly more variable than that observed with the 200-mg dose. Between 375 and 700 mg of ciprofloxacin reached the systemic circulation after administration of the 750-mg dose, with no evidence of adverse reactions.