Purpose: Anaesthesia routinely is used in animal neuroimaging in order to reduce head motion artefacts and minimize the influence of stress. However, anaesthetics can modify radioligand binding profiles at receptor targets studied by positron emission tomography (PET). Here, we determined the effects of two routine anaesthetics on the binding of a tracer of the serotonin 5HT_2A receptors. Procedures: Isoflurane- and propofol-anesthetised Göttingen minipigs were imaged with [¹¹C]MDL100,907 PET and analysed using regions of interest and statistical non-parametric mapping. Results: The binding potentials of the tracer in striatum under isoflurane anaesthesia significantly exceeded those obtained under propofol anaesthesia, an effect we attribute to the higher blood flow in brain induced by the former. Conclusions: Interactions between radioligands and anaesthesia must be carefully evaluated in the design of in vivo neuroimaging and interpretation of data.