Harmine, harmaline, tetrahydroharmine (THH), and N,N-dimethyltryptamine (DMT) were quantitated in plasma from 15 healthy male volunteers after the ingestion of ayahuasca, a beverage that has been used for religious purposes in Brazil since pre-Columbian times. A growing awareness of the interest in this ancient shamanistic practice in modern urban cultures and the widespread popular dissemination of the inebriant effects and type and sources of the plant admixtures used to prepare the beverage have provided additional impetus for this study. The three harmala alkaloids were quantitated from protein-precipitated plasma by high-performance liquid chromatography using fluorescence detection. Recovery from blank human plasma was quantitative, and the limit of quantitation (LOQ) was below 2 ng/ml of plasma for each of the harmala alkaloids. Standard concentrations ranged from 10 to 250 ng/ml for harmine and THH and from 1.0 to 25.0 ng/ml for harmaline, respectively. linearity was observed for harmine, harmaline, and THH within these respective ranges. The highest concentrations of harmala alkaloids in human plasma were found to be 222.3 ng/ml for harmine, 134.5 ng/ml for THH, and 9.4 ng/ml for harmaline. DMT was quantitated by gas chromatography using nitrogen-phosphorus detection after liquid-liquid extraction with diphenhydramine as an internal standard. DMT recovery was quantitative, and the limit of detection and lOQ were 0.5 and 5 ng/ml, respectively. linearity for DMT was observed from 5 to 1000 ng/ml. The one-step extraction method for DMT and the protein precipitation method for the three harmala alkaloids afford rapid, sensitive, and quantitative analyses of these alkaloids with minimal analyte loss. The analytical methods also may be applicable to other matrices, including whole blood and urine samples and homogenized tissue specimens. These are the first reported observations of DMT and harmala alkaloids in plasma after ritual ingestion of ayahuasca.