In order to determine the relevance of low vitamin B12 concentration in elderly persons (greater than 65 years), serum vitamin B12 levels were measured in 292 consecutive patients upon their admission to a geriatric ward. Eighty (27%) of them were anaemic (haemoglobin less than or equal to 7.14 mmol/l). The vitamin B12 concentration was not statistically different between males and females, nor between the anaemic and non-anaemic groups. Twenty-two patients (7.5%) had a low vitamin B12 level; of these, 10 had a haemoglobin concentration higher than 7.14 mmol/l and a mean corpuscular volume lower than 98 fl. In addition, serum vitamin B12 levels were also measured in 178 consecutive anaemic patients hospitalized in the same ward. Seventeen (9.5%) of them had a vitamin B12 deficiency although in 11 the MCV was lower than 98 fl. Hypersegmented polymorphonuclear leukocytes were rarely observed in the peripheral blood smear. Pernicious anaemia could only be diagnosed in 1 patient. Serum vitamin B12 estimation may be necessary to detect vitamin B12 deficiency but a low level requires additional diagnostic investigation.