Anaemia of uncertain origin is common in elderly people and is reported to be more common in men than women. We have investigated retrospectively a database of haematological and biochemical data on 16.332 people referred to an outpatient laboratory and compared the blood haemoglobin (Hb) concentration of the sexes. In men the mean adult Hb values of 151 g/1 started to decline at the age of 60 to reach the level of 138 g/1 by the age of 80 and older. In women, by contrast, the mean adult Hb concentration of 134 g/1 started to increase at the age of 50 to 137 g/1 then declining after the age of 70. A multiple regression analysis of variables likely to influence measured Hb values indicated that 6,7 g/1 of the observed 13 g/1 decrease in elderly men could not be explained by chance or selection bias and that an increase of Hb values in women was sustained until after 80 years of age. Results would suggest that sex or sex hormone related factors influence haemoglobin concentrations in elderly people.