It is known that pernicious anaemia is sometimes associated with mental symptoms which improve following vitamin B12 therapy (Eilenberg, 1960; Holmes, 1956; Smith, 1960). Further, it has been pointed out that such mental symptoms can occur years before the development of anaemia and no definite relationship exists between them and the severity of anaemia (Smith, 1960). Cases have been described with a variety of psychiatric symptoms and low serum vitamin B12 levels without any neurological manifestation or abnormality of peripheral blood and bone marrow. Since pernicious anaemia is due to vitamin B12 deficiency it is suspected that B12 deficiency is responsible for the mental symptoms, and serum B12 assays have been advocated routinely in psychiatric patients (Strachan and Henderson, 1965; Hunter and Matthews, 1965).