A rapid, sensitive, reliable quantitative GC/MS method using 0.2 mL of urine was developed for the confirmation of cocaine use. After a simple organic solvent extraction and derivatization with pentafluoropropionic anhydride, cocaine, benzoylecgonine, and ecgonine methyl ester were identified by GC/MS through the retention time for the total ion current and selected ion monitoring (SIM) for each analyte. Quantitation was achieved by obtaining the calibration curves for the molecular ion ratios of the analyte/ketamine (IS) over a range of 12.5-250 ng/mL (0.1-2 ng total). The extraction efficiency for these analytes ranged from 70 to 82%. The sensitivity limit of detection for each analyte was 12.5 ng/mL (0.1 ng) at p less than 0.01. Intra- and interday precision for these analytes ranged between 14.7 and 29.5% CV. This method is in routine use in our laboratory for the GC/MS confirmation of enzyme immunoassay cocaine-positive urine samples.