An accurate, simple, reproducible and sensitive method for the determination of acetylsalicylic acid, caffeine and codeine phosphate has been developed and validated. Acetylsalicylic acid, caffeine and codeine phosphate were separated using a mu Bofidapack C-8 column by isocratic elution with flow rate 1.0 ml/min. The mobile phase composition was 125/125/250/0.5 (v/v) isopropyl alcohol, acetonitrile. water and omicron -phosphoric acid. The samples were detected at 215 nm using photo-diode array detector. The linear range of detection for acetylsalicylic acid, caffeine and codeine phosphate were between 0.40 and 1000, 0.25 and 250, and 0.48 and 96 mug/ml, respectively. The linearity, range, selectivity, system performance parameters, precision, accuracy, and ruggedness for acetylsalicylic acid, caffeine and codeine phosphate were also shown to have acceptable values. (C) 2001 Elsevier Science B.V. All rights reserved.