A method is presented for the simultaneous identification and quantification of several CNS stimulants, including amphetamine in plasma and urine by GC/FID using mephentermine as an internal standard. No derivation is necessary and after a single alkaline extraction, GC analysis for the 11 compounds tested is achieved in 23 min. The lower limit of detectability was found to be 4 ng/ml for amphetamine in plasma. This method is sensitive, reproducible, selective and applicable in forensic and clinical toxicological analyses. Toxicological findings, after a fatality involving phendimetrazine are presented as an application of the procedure.