A low supply of iron in the diet may result in iron deficiency and mild iron-deficiency anaemia in healthy individuals. Women are more susceptible than men because of menstrual iron loss. We compared the effect of a low dose of iron, administered as a dietary supplement, with a high pharmacological dose of iron to otherwise healthy individuals with iron deficiency and mild iron deficiency anaemia.In a randomised, double-blind trial conducted in 2000-2001, 73 women and three men with iron deficiency received either 27.6 mg of iron consisting of ferrous fumarate enriched with 13% haem iron, or 100 mg ferrosulphate daily for 12 weeks. Blood samples were analysed four times in the course of the treatment.The median ferritin value rose by 13 and 7 μg/l in the high-dose and low-dose group, respectively. The increase in ferritin was significantly higher in the high-dose than in the low dose group ( < 0.001). There was no statistically significant difference between the groups in the change in Hb, serum-iron or serum-iron binding capacity. The median haemoglobin value increased by 0.4 g/100 ml in both groups. Gastrointestinal side effects were experienced by 58% in the high-dose group and 35% in the low-dose group. Four subjects in the high-dose group and one in the low-dose group broke off the treatment because of side effects.A supplement of low-dose iron is enough to increase iron stores in cases of nutritional iron deficiency in healthy individuals and to optimise haemoglobin. High-dose iron caused the largest increase in iron stores. Low-dose iron resulted in the least side effects.