Gas-liquid chromatographic determination of nanogram quantities of chlorpheniramine maleate (CP-M) and dl-methylephedrine hydrochloride (ME-HCl) in antipyretic and analgesic preparations was examined. Prescribed amounts of CP-M and ME-HCl in the preparations are 0.4-1.5 mg and 2-5 mg, respectively. Rubidium chloride alkali flame ionization detector was more sensitive for nitrogencontaining compounds than normal flame ionization detector and could easily detect 40 ng of CP-M which showed 30% of the peak height of full scale without base line drift or noise. Each base was extracted from alkaline aqueous solution with benzene containing internal standard. It Noscapin was prescribed for the preparation, it was necessary to decompose it in sodium hydroxide solution by warming at 50°for 30 min and extraction with benzene because Noscapin has a long retention time and interferes the routine analysis of CP-M and ME-HCl. Benzene layer (1.0 μl) was injected into the gas chromatograph. Internal standards used were N-butyryl-o-toluamide for ME-HCl and diphenylpyraline for CP-M. Gas chromatographic conditions were : 3.5% JXR on Chromosorb G (80-100 mesh, acid-washed and silane-treated), glass column (2.5 mm×2 m) at a temperature of 180°, nitrogen as a carrier gas at the flow rate of 30 ml/min, and using RbCl alkali flame ionization detector.