Using GC/MS in scanning mode as a screening and definitive identification methodology for substance abuse testing, 4500 urine samples have been analyzed. The accuracy and sensitivity of this method was evaluated by the results of 92 proficiency sample analyses, reanalyses by TLC screening with GC confirmation of 125 samples from forensic sources and reanalysis by EMIT screening for seven groups of drugs confirmed by GC/MS of 590 samples from industrial and treatment sources. The results of these studies are presented.