A review is given of the principles, some possibilities and limitations of single photon and positron emission tomography, SPECT and PET, respectivily. The article covers thus far published results in the field of schizophrenia. Concerning the pathogenesis of the disease particular emphasis is given to the concept of hypofrontality and dopamine receptor overactivity. Concerning hypofrontality both supporting as well as refuting data have been published when patients were investigated during resting conditions. Yet, the prefrontal cortex seems to be substantially less activitated during performance of specific cognitive tasks in patients as compared to normals. Regarding dopamine receptor activity the scientific debated hasn't ceased yet, but there is a growing consensus that non- (or never) medicated schizophrenic subjects have no elevated receptor densities. Much research has been aimed at the binding properties of antipsychotic drugs to dopamine- (D- en D-) and serotonine-(5HT) receptors. These studies resulted in new opinions on the mechanism of action of these drugs and the dopamine hypothesis.