The first case involving an alleged sexual assault linked to the use of gamma-hydroxybutyric acid (GHB) in Oklahoma is reported. A-48-year-old Caucasian woman taking amitriptyline was known to have voluntarily ingested a sports drink containing a relaxing health product. She purportedly experienced unconsciousness that persisted for approximately 4 h. The toxicological testing on urine identified GHB, amitriptyline, and nortriptyline using a capillary Hewlett-Packard 6890 gas chromatograph coupled to a Hewlett-Packard 5973 mass selective detector (MSD). The GHB concentration in urine was 26.9 microg/mL. Urine concentrations of amitriptyline and nortriptyline were not determined. The analytical method used for identifying and quantitating GHB can be applied to matters of forensic interests.