A simple HPLC method with ultraviolet detection of ciprofloxacin in human plasma was developed and validated. After protein precipitation with trichloroacetic acid, chromatographic separation of ciprofloxacin in plasma was achieved at $50^{circ}C$ with a $C_{18}$ column and methanol-phosphate mixture (pH 2.5), as mobile phase. Quantitative determination was performed by ultraviolet detection at 278 nm. The method was specific and validated with a limit of quantification of 100 ng/ml. The intra- and inter-day coefficients of variation were between 1.67% and 10.55% and accuracy between 92.01 % and 106.09%. The method has been successfully applied in a bioavailability study of 250 mg ciprofloxacin hydrochloride tablet.