Sixty consecutive patients with progressive intellectual deterioration were evaluated by a specific protocol. Eighteen (30%) were found to have an underlying disease potentially reversible by medical or surgical therapy. Sixteen patients had a specific diagnosable but untreatable disease as a cause of dementia. The laboratory and radiologic tests of the protocol that uncovered treatable illnesses were the radioisotope brain scan (two cases of bilateral subdural hematoma), the pneumoencephalogram (seven patients with normal-pressure hydrocephalus), thyroid function screen, and liver function studies (one case each). Unrewarding tests included serum barbiturate, bromide, vitamin B12, and folate levels.