We investigated the haematological effects of a massive dose of oral cobalamin (vitamin B12) on patients with cobalamin deficiency anaemia who had severe anaemia with a few neurological impairments and found that oral treatment was almost as effective as conventional injection therapy. The recovery of haematological indices with oral cobalamin preparations was slightly slower than with parenteral preparations, although the subjective symptoms disappeared soon after the start of therapy. The results of this study indicate that oral treatment keeps the cobalamin body stores satisfactorily filled and might be useful for older patients in whom injecting might be difficult.