The simultaneous determination of the active ingredients in a multicomponent pharmaceutical product is reported. Pseudoephedrine HCl (I), guaifenesin (II) and dextromethorphan HBr (III) were separated and quantitated simultaneously in a cough syrup by HPLC using an isocratic, reverse-phase system. The column consisted of a octadecylsilane 5-micron stationary phase. The mobile phase was 45% (v/v) aqueous methanol with ammonium formate as buffer (pH 4.3). The retention times were approximately 4.50, 7.30 and 17.60 minutes for (I), (II) and (III), respectively. The method is repeatable and reproducible.