A gas chromatographic-mass spectrometric procedure for detection of cathinone (Khat) and methcathinone (CAT) in urine was developed. The compounds were detected as 4-carboethoxyhexafluorobutyryl derivatives. Three ions for the drugs and two ions for the internal standards were monitored. The drugs were identified by comparing retention times and ion ratios with that of reference compounds. The concentrations were measured by using amphetamine-d6 as internal standard for cathinone and methamphetamine-d9 as internal standard for methcathinone, and were linear over the range of 25-5000 ng/mL for cathinone and 12.5-5000 ng/mL for methcathinone. The overall recoveries of cathinone and methcathinone were 86 and 78%, respectively. Intrarun and inter-run variations were < 20%. To verify that the drugs are not metabolites of over-the-counter medications, cathinone and methcathinone were tested in urine specimens collected from individuals who ingested phenylpropanolamine and pseudoephedrine. None of the specimens showed the keto-amines as the metabolic products. When the procedure was applied to test 66 amphetamine-immunoassay-positive specimens containing no amphetamine or methamphetamine, two specimens were found positive for cathinone (118 and 3266 ng/mL) and six specimens were found positive for methcathinone (13-91 ng/mL).