The Syva Emit stm Urine Amphetamine Assay qualitatively determines the presence of uri-ne amphetamine，one sample at a time. In each test，one sample and one calibrator are sayed together to compare the reaction rates. This method is ii^fRcient and expensive. Etetailed analysis of the reaction kinetics of the Emit® st1M Urine Amphetamine reagents indicated that the reaction kinetics were relatively linear up to 15 minutes after the initiation of the reactions. Hiis makes it possible to assay multiple samples with a single calibrator. A nidified protocol is described which analyzed three samples with each calibrator, a modification leading to savings of one -third of the reagents and cost，with no compromise in assay performance. Addition of an extra 2 ml of distilled water to the regular protocol can lead to even more savings.