Ketamine can be used to facilitate date-rape when unknowingly spiked into a victim's beverage. If a biological sample is not available from the victim, the beverage container might be the only remaining source of forensic evidence. We present a rapid, simple analysis method for the detection of ketamine in wet or dry beverage residues based on liquid chromatography-mass spectrometry (LC-MS). Wet residues consist of the final few drops (<1 ml) in a container while dry residues are the remains once all liquid has evaporated. By using LC-MS, which readily handles aqueous samples, often no derivatization or sample extraction is needed, thus reducing analysis time and lab technician involvement. Tandem mass spectrometry (MS/MS) provides an enhancement in both selectivity and sensitivity. We have studied a range of beverages and determined limits of detection between 1.2 × 10-3 and 1.3 × 10-4 mg/ml, compared to 0.21-0.85 mg/ml used in most date-rape scenarios. This paper represents the first published report of using LC-MS/MS for the analysis of beverage residues for the presence of a date-rape drug. This method could replace the current gas chromatography-mass spectrometry (GC-MS) methods and provide a faster, more selective method for the analysis of date-rape drugs, requiring virtually no sample preparation.