Routine methamphetamine testing identified a urine specimen with inconsistent screening and confirmation results. The methamphetamine RIA screening test (Diagnostic Products Corporation) indicated a borderline positive specimen, while the achiral confirmatory GC/MS result showed 4690 ng/mL of methamphetamine and 1895 ng/mL of amphetamine. Analysis of the specimen after derivatization with S(-)-N-trifluoroacetylprolyl chloride showed only the presence of 1-amphetamine and 1-methamphetamine. It was later learned that the individual providing the specimen had been taking Selegiline. Selegiline, (-) propynylmethamphetamine, is a monoamine oxidase inhibitor used for the treatment of Parkinson's disease. It is sold under the trade name Eldepryl. Its major metabolites are 1-methamphetamine, 1-amphetamine and N-desmethylselegiline. Urine specimens from other Selegiline users were obtained and analyzed. A characteristic metabolic pattern was noted, exemplified by a ratio of 1-methamphetamine to 1-amphetamine of about 2.8. This is in contrast to what is observed in the urine of individuals who ingest pure 1-methamphetamine, such as with Vicks Inhaler, where the 1-methamphetamine to 1-amphetamine ratio in the urine is usually greater than 8. Caution is advised when interpreting methamphetamine results without using a chiral identification technique.