Laboratory results and bone marrow appearances for the cases presented. Case 1 shows a normal serum vitamin B-12 concentration with biochemical features of B-12 deficiency (raised homocysteine and methylmalonic acid). The haematology indices (macrocytic anaemia) and bone marrow appearances are consistent with megaloblastic anaemia caused by classic pernicious anaemia, confirmed by a positive anti-intrinsic factor antibody. Case 2 shows a markedly reduced serum vitamin B-12 concentration but largely unremarkable biochemical features (normal homocysteine concentration and slightly raised methylmalonic acid) of vitamin B-12 deficiency. The mild anaemia and reduced mean cell volume are consistent with a β thalassaemia trait, and the bone marrow appearances are normal