We have measured concentrations of ciprofloxacin in serum, hepatic tissue, gallbladder, and bile in 10 patients after a single oral dose of 750 mg given before cholecystectomy. Mean liver and gallbladder tissue concentrations were 12.76 micrograms X g-1 +/- 2.79 (SEM) and 5.94 micrograms X g-1 +/- 1.35, respectively. Concentrations in bile taken from the gallbladder (7 patients) ranged from 68 to 225 micrograms X ml-1, with a mean bile/serum concentration ratio of 49. Concentrations in bile taken from the common bile duct (2 patients) were 17 and 16 micrograms X ml-1.