Of 20 women (pre-menopausal) with iron deficiency anaemia, only three felt that their periods were unduly heavy. However, on objective assessment of menstrual loss using the alkaline haematin method, the blood was found to be excessively heavy in 12 cases (296 +/- 45 mls per cycle: normal is 80 mls/cycle). The findings emphasise that women underestimate the extent of menorrhagia.