Anterior pituitary functions and sex steroid levels were measured in 12 patients with idiopathic haemochromatosis (eight males, four postmenopausal females) and age-matched controls, 12 with diabetes mellitus and five with hepatic cirrhosis. In idiopathic haemochromatosis gonadotrophin deficiency was present in seven of 12 patients including six of seven patients who had clinical evidence of hypogonadism. Basal prolactin levels were significantly lower in the patients with idiopathic haemochromatosis compared with either of the control groups (p less than 0.02). Nine patients with idiopathic haemochromatosis exhibited subnormal prolactin responses to thyrotrophin releasing hormone. Thyroid and adrenocortical functions were normal in all patients with idiopathic haemochromatosis. Testosterone values were subnormal in five of eight males with idiopathic haemochromatosis; females with idiopathic haemochromatosis had significantly lower testosterone values compared with the diabetic females (p less than 0.05). Oestradiol values in both sexes and sex hormone binding globulin values in the males were not significantly different in patients with idiopathic haemochromatosis compared with the controls. Sex hormone binding globulin levels were significantly higher in females with idiopathic haemochromatosis compared with either diabetic or cirrhotic females (p less than 0.05). Impairment of anterior pituitary function occurs in idiopathic haemochromatosis but is selective; gonadotrophin and prolactin deficiencies are common. Clinical hypogonadism is usually hypogonadotrophic in origin.