Rapid and accurate analytical testing can be of great value when determining treatment for pediatric patients suspected of ingesting an unknown chemical. Though often overlooked, gas chromatography/mass spectroscopy (GC/MS) can be a valuable resource in emergency toxicology testing. In a recent 24-month period (July 1999-June 2001), the Analytical Toxicology Laboratory at the University of Mississippi Medical Center, Jackson, MS, compared the results of GC/MS analysis to results obtained by immunoassay testing. The laboratory tested 139 urine samples referred for STAT toxicology testing from the hospital's Pediatric Emergency Department. All samples were tested in parallel using an immunoassay technique (EMIT) and GC/MS. With analysis by immunoassay, 17.3% of the samples were positive for a drug of abuse. The number of positive drug classes ranged from 0 to 2 per sample (mean 0.17 +/- 0.43) using immunoassay. With analysis by GC/MS, drugs were detected in 88.5% of the samples. The number of drugs detected ranged from 0 to 11 per sample (mean 2.2 +/- 1.8) with GC/MS. A total of 64 different pharmaceuticals were identified by GC/MS. This study shows that analysis by GC/MS offers the clinician a more comprehensive view into the exposure of the pediatric patient presenting with an unknown chemical ingestion.