A sensitive and specific quantitative assay for the determination of dextromoramide in human fluids and tissues is described. Dextromoramide and an internal standard, SKF 525 A, are isolated by a basic extraction and back-extraction process. The final extract is separated on a 25-m capillary column B.P. 1 and drugs are detected by selected ion monitoring at m/z 100 and m/z 86 for dextromoramide and the internal standard, respectively. The minimum detectable quantities are 0.5 and 0.3 ng/mL, for dextromoramide in plasma and urine, respectively. Coefficients of variation for within-run data were less than 6%.