We have carried out a single-dose comparison of three different dextromethorphan cough mixtures in 10 healthy human volunteers. Dextromethorphan was administered in a single dose of 60 mg in random order. The concentrations of dextromethorphan and its main metabolite, dextrorphan, were determined from the plasma samples using high performance liquid chromatography. The concentrations of dextrorphan were 170 times higher than the concentrations of dextromethorphan. No therapeutically significant differences were detected between the three preparations tested, and there were no great differences between the pharmacokinetic profiles of dextromethorphan and dextrorphan. The three test preparations were Resilar and Redol comp. (Remeda Pharmaceutical Co., Finland), and Extuson (Ferrosan Ab, Sweden).