Among a total of 1,400 examined cases, the positrocephalogram (PCG) allowed correct localization in 77% of the patients with a brain tumor. The diagnostic safety for the exclusion of an expansive process varied from 76% to 87%. By associating the data obtained through angiography with those furnished by the PCG it has been possible to establish a precise site diagnosis in 97% of the cases of brain tumor. Additional substantial improvement was attained as far as the diagnosis of the tumor type is concerned. When associated with the EEG, the PCG represents such a marked improvement in policlinical diagnosis that, as a rule, if the results of the neurological examination, the EEG, the PCG and plain radiology are negative for tumor, it is valid to give up further contrast methods. This mainly eliminates the overchange represented by patients with convulsive disorders as, up to now, diagnostic research in order to exclude a brain tumor in such cases was only possible with safety by means of stationary observation.