A sensitive and specific quantitative method for the determination of zipeprol, a newly abused antitussive, in human fluids is described. Zipeprol and an internal standard, levallorphan, are isolated by a basic extraction and back-extraction process. The final extract is derivatizated with BSTFA + 1% TMCS and separated on a 12-m HP-1 capillary column. Drugs are detected by selected ion monitoring at m/z 335 and m/z 355 for zipeprol and the internal standard, respectively. The minimum detectable quantities are 0.6 and 0.4 ng ml-1, for zipeprol in plasma and urine, respectively. Relative standard deviations for within-run data are less than 6%.