Localization of Hg203-labeled Neohydrin in studies of the brain has been demonstrated in various non-neoplastic processes and the scan configuration has shown certain distinguishing features. By using the principles of classification sug-gested, useful information concerning non-neoplastic abnormalities is obtained. The Class V scan is considered positive for neoplasm. Scanning has proved an effective screening method in exclusion of neoplasm in Classes I through III. As with all studies, however, it must be tempered with clinical judgment, as a few neoplasms will be seen in these groups. A Class IV pattern is an indication for additional study, as this most often represents neoplasm. Accuracy of scans so classified compares favorably with other neuroradiological procedures, without the their attending morbidity.