Vapor phase methodology for quantitative analysis of urine for metanephrine and normetanephrine as the pentafluoropropionyl derivative is described. The use of selected ion monitoring provided sufficient sensitivity and selectivity that milliliter aliquots of urine required only a simple scheme of sample processing; preliminary purification consisted of percolation through a column of XAD-2 followed by solvent extraction. The sample extracts were converted to the pentafluoropropionyl derivatives and analyzed by gas chromatography mass spectrometry with selected ion monitoring. Quantitative analysis was based on alpha[2H2]-beta-[2H1]metanephrine and alpha-[2H2]-beta-[2H1]normetanephrine which were added to the urine sample at the outset. The calibration plots for metanephrine and normetanephrine were linear from 10 ng ml-1 to 2000 ng ml-1 of urine permitting the detection of metanephrine and normetanephrine levels throughout the normal range and well into the subnormal range. Examples of application of the methodology to clinical investigation are described. The overall reproducibility of the sample processing methodology and instrumentation was assessed by replicate analyses of the same urine sample over a period of several weeks; the coefficient of variation was +/- 2.5% (n = 8).