In traditional South-American practice, the action of the herbal hallucinogen 5-methoxy-N,N-dimethyltryptamine (MeO-DMT) is potentiated by co-administration of a herbal monoamine oxidase (MAO) inhibitor, a phenomenon known as the ayahuasca effect. However, little is known about the pharmacology of MeO-DMT. In order to investigate the basis for the ayahuasca effect, we developed a radiosynthesis of [11C]MeO- DMT and mapped its distribution in brain of living pigs by positron emission tomography (PET). Relative to the metabolite-corrected arterial input, [11C]MeO-DMT had a distribution volume (Vh) in the range of 3 – 7 mL/g. The highest binding of [11C]MeO-DMT was in the ventral striatum, partly resembling the distributions of the MAO ligand [11C]harmine and the dopamine receptor ligand [11C]raclopride. Pharmacological challenges were tested in groups of three pigs. Co-injection with excess non-radioactive MeO-DMT (mean dose 1.7 mg/kg) did not attenuate cerebral binding but rather increased the magnitude of Vh globally by 20–30%. Co-injection with the serotonin 5HT2 antagonist ketanserin (mean dose 0.8 mg/kg) unexpectedly increased [11C]MeO-DMT Vh by 5 – 10% throughout brain. Pretreatment with the MAO inhibitor pargyline (5 mg/kg) at 30 – 60 minutes prior to the second tracer injection reduced the Vh globally by 10%. The results indicate an absence of a significant serotonin 5HT2 binding component for [11C]MeO-DMT in living brain. Cerebral [11C]MeO-DMT binding may be associated with MAO, non-5-HT2 serotonin receptors, or dopamine receptors.