A reverse phase high performance liquid chromatography (HPLC) method was developed for the simultaneous determination or codeine (methyl morphine) and dionin (ethyl morphine hydrochloride) in antitussive analgesic tablet formulations. A C-18 column and methanol-water (1:2) mixture mobile phase (pH 3.0) were used. Spectrophotometric detection was carried out at 210 nm. The total elution time was shorter than 7 min. This method was found to be quite precise and reproducible. This proposed method was successfully applied to the determination of codeine and ethyl morphine hydrochloride in tablets produced by the Turkish Army Drug Factory. (C) 2001 Elsevier Science B.V. All rights reserved.