Dementia is a symptom complex probably arising from cerebral metabolic insufficiency. The testing of drugs thought to improve cerebral metabolism is difficult and many problems have to be overcome. Assessment of brain failure requires objective tests of intellect and memory. Subjective tests are used for disorders of personality and affect. The most useful and practical tests are described in detail. Clinical trials have to be double-blind with strict control of all factors which may influence the tests. Hydergine has been tested in 1,300 patients and shown to be an effective therapeutic agent.