The dietary sugar of 15 young men was reduced from their habitual approximately 150 g/day to about 55 g/day. After 3 weeks, the concentration of oestradiol in their plasma fell by about 25%. Resumption of their habitual intake of sugar for 2 weeks restored the oestradiol concentration to its previous value. The results provide further evidence that dietary sugar can be one of the causes of coronary heart disease, and support the view that the underlying mechanism producing the disease is a disturbance in hormone balance.