We introduced a new combined method to isolate, purify and quantify oxoacids in human urine. Preparation of O-(2,3,4,5,6-pentafluorobenzyl) oximes of oxoacids at pH 2 to 3 was followed by cation-exchange column chromatography for removing the biological interferences. The effluent with water was extracted with ethyl acetate and the oxoacids were quantitatively converted into their trimethylsilyl derivatives for detection by gas chromatography-mass spectrometry. Good quality control data were obtained through precision and accuracy tests. Analytical recoveries (53.5-99.8%) were quantitative for a wide variety of oxoacids. This method was used for the measurement of 18 oxoacids in the urine of healthy volunteers.