Diurnal Variations of the Serum Iron in Normal Subjects and in Patients with Haemochromatosis

S ummary . A definite diurnal variation in serum iron exists in normal subjects, in which the serum iron levels are highest in the morning or at noon, and then gradually fall throughout the day to reach their lowest values in the evening; the serum iron concentration rises again the following morning after sleep. The diurnal rhythm may be regulated by the activity of the reticulo‐hypothalamic system, which may be under the influence of neurogenic or hormonal factors. Contrary to other workers, there is a definite diurnal variation in the serum iron concentration in patients with idiopathic haemochromatosis.