Introduction – Tetrapterys mucronata Cav. (Malpighiaceae) is a plant used in some regions of Brazil in the preparation of ayahuasca. Objective – To determine the content of the main tryptamine alkaloids in the stem bark of T. mucronata Cav. and assess their possible toxic and hallucinogenic properties based on the doses found in a water decoction that mimics the ayahuasca preparation. Methods – Four alkaloids previously described for their toxic and hallucinogenic properties were quantitated by multiple reaction monitoring HPLC combined with electrospray ionisation and tandem MS (HPLC–ESI/MS/MS) in the water decoction and ethanolic extracts from the bark of T. mucronata. Results – Exhaustive extraction of the stem barks with ethanol revealed the following alkaloid levels: bufotenine (1) 3.26 ± 0.31 mg/g, 5-methoxy-N-methyltryptamine (2) 0.88 ± 0.08 mg/g, 5-methoxy-bufotenine (3) 3.07 ± 0.22 mg/g and 2-methyl-6- methoxy-1,2,3,4-tetrahydro-β-carboline (4) 0.14 ± 0.004 mg/g. The water decoction presented slightly lower levels, ranging between 2.32 ± 0.14, 0.50 ± 0.04, 1.53 ± 0.09 and 0.10 ± 0.01 mg/g for (1), (2), (3) and (4) respectively. Conclusions – The HPLC–ESI/MS/MS quantitation revealed significant alkaloid levels, in particular for bufotenine and 5- methoxy-bufotenine. As such compounds are known for their toxic and hallucinogenic properties, these results indicate that the consumption of this plant as an ingredient in ayahuasca preparations may present a risk to consumers.