Rats and mice are often anesthetized prior to positron emission tomography (PET) brain imaging in order to prevent head movements. Anesthesia can be administered by injection mixtures, such as fentanyl-fluanisone-midazolam or inhalation agents, such as isoflurane. Unfortunately, anesthesia affects a variety of physiological variables, including in the brain. The aim of this study was to compare the effects of inhalation and injection anesthesia on the binding potential of the dopaminergic D2/3 tracer [11C]raclopride used for PET brain imaging in human and animal studies. Male Lewis rats were assigned to either injection (fentanyl-fluanisone-midazolam; N=5) or inhalation (isoflurane; N=4) anesthesia. After a short attenuation scan, the rats were PET scanned for 90 minutes after injection of [11C]raclopride. We found that rats anesthetized with isoflurane had double the binding potential in the striatum compared with fentanyl-fluanisone-midazolam anesthetized rats. Our results are in agreement with other studies showing that anesthesia may have a major influence on brain imaging studies involving tracer kinetics in rats.