1. The pharmacokinetics of ciprofloxacin were determined in 8 healthy young volunteers (5 men and 3 women) after administration of single oral doses of 250 mg. 2. The peak plasma concentration of ciprofloxacin (Cmax = 1.26 +/- 0.21 mg/l), the time to reach Cmax (Tmax = 1.99 +/- 0.26 h), the area under the time-plasma concentration curve (AUC = 5.52 +/- 0.84 mg h l-1), the terminal phase half-life (T1/2 = 3.05 +/- 0.56 h), the volume of distribution (Vd/F = 195.4 +/- 14.0 l) and total body clearance (CL/F = 46.3 +/- 2.6 l/h), both expressed as functions of the oral bioavailability (F) of ciprofloxacin were within the corresponding values reported in the literature for other healthy population groups. 3. Multiple dose administration (250 mg, po, twice daily for 4 days) did not result in accumulation of ciprofloxacin in plasma. No adverse side effects occurred during the study. 4. The pharmacokinetic data are discussed in relation to the minimum inhibitory concentration (MIC) of ciprofloxacin for a number of common pathogens isolated from human infections in Rio de Janeiro.