Ovarian volume and the diameter of the intra-ovarian follicles correlated with the percentage of premorbid weight in 36 patients with anorexia nervosa who had repeated pelvic ultrasound scans during weight gain. Oestradiol levels increased when the follicles became dominant and were greater than 1 cm in diameter; and uterine growth increased linearly with plasma oestradiol. Pelvic ultrasonography can thus be used as a simple, rapid, bioassay to determine hypothalamic-pituitary-ovarian function in patients with anorexia nervosa and provides a useful guide to the degree of weight restoration required to enable menstrual function to cover. The outcome of anorexia nervosa may be related to the degree to which the biological consequences of starvation which perpetuate the disorder are overcome. The menstrual abnormalities in bulimia nervosa are associated with pelvic ultrasound findings such as small multifollicular ovaries and small uterine areas which also occur in anorexia nervosa and simple weight loss amenorrhoea. This suggests that weight loss or the nutritional disturbance in bulimia nervosa may underlie the menstrual irregularities which commonly occur in this condition.