A simple high-performance liquid chromatography method has been developed for the determination of naproxen in human plasma. The method was validated on an Ace C18 column using ultraviolet detection. The mobile phase consisted of 20 mM phosphate buffer (pH 7) containing 0.1% trifluoroacetic acid-acetonitrile (65:35, v/v). The calibration curve was linear between the concentration ranges of 0.10 and 5.0 mu g/mL. Intra-day and inter-day precision values for naproxen in plasma were less than 4.84, and accuracy (relative error) was better than 3.67%. The extraction recovery values of naproxen from human plasma were between 91.0 and 98.9%. The limits of detection and quantification of naproxen were 0.03 and 0.10 mu g/mL, respectively. Also, this assay was applied to determine the pharmacokinetic parameters of naproxen in six healthy Turkish volunteers who had been given 220 mg of naproxen.