For many years, cases of pernicious anaemia associated with mental symptoms have been described, and interest in these symptoms was renewed following the introduction of liver therapy (Richardson, 1929; Phillips, 1931). Interest later appeared to decline, so that MacDonald Holmes (1956), almost 20 years after the last important clinical review of the subject, could comment with justification that although the cerebral lesions of pernicious anaemia had been recognized for more than a century they were still much less familiar than the lesions which occurred in the spinal cord and peripheral nerves. Since then vitamin B12 deficiency as a cause of mental symptoms has given rise to increasing interest, and this is reflected in recent suggestions that serum vitamin B12 assays should be carried out routinely in psychiatric patients and might be more informative nowadays than the routine Wassermann reaction (Strachan and Henderson, 1965; Hunter and Matthews, 1965).