The responses of pituitary hormones and venous catecholamine concentrations to insulin hypoglycaemia were studied in 12 formerly obese women with familial obesity who had lost about 30 kg by dieting. These responses were compared with those of 10 lean women. The post-obese women showed an exaggerated response in cortisol output but an impaired release of growth hormone. 6 of the post-obese women had in addition both an impairment in prolactin output and a failure to increase their venous noradrenaline concentrations during hypoglycaemia. These results suggest that an alteration in hypothalamic control, displayed by limited responses in pituitary hormone secretion and by reduced sympathetic activity, may be an innate feature of people with familial obesity