A rapid, specific, high-pressure liquid chromatographic method is presented for the determination of viloxazine in plasma and urine. This method employs the high sensitivity of fluorescence detection with selective extraction and reversed-phase chromatography to measure concentrations as low as 25 ng/ml of plasma and 1.0 microgram/ml of urine. Known metabolites of viloxazine do not interfere with the analysis, and experience with several hundred samples in a bioavailability study demonstrated the applicability and reliability of the method.