We have previously reported an impaired growth hormone (GH) response and abnormal prolactin release to insulin-hypoglycaemia in obesity. We suggested that obese women with an absent prolactin response to hypoglycaemia (‘non-responders’) have a disorder of hypothalamic function. We have now investigated the GH response to i. v. growth hormone releasing factor, GHRF (1–29)NH2, in 14 obese women and nine age-matched normal-weight women. We found a significantly reduced GH response to GHRF in the obese women as compared with controls (mean peak · SEM: obese 8·9 · 2 mu/l, controls 28 · 2 mu/l; P >0·01). When the obese women were divided on the basis of their prolactin response to insulin-hypoglycaemia (seven ‘non-responders’, mean weight 102 · 5 kg; seven responders, mean weight 108·8 kg) a similar GH response to GHRF was found between the two groups but the GH response to hypoglycaemia was significantly less in the ‘non-responder’ women (mean peak ‘non-responders’ 10·5 · 3 mu/l, responders 27·4 mu/l; P < 0·05). We conclude that obesity may be characterized by an impaired GH response to both i. v. GHRF and insulin-hypoglycaemia, which suggests altered hypothalamic-pitui-tary function. The finding that the GH response to hypoglycaemia is significantly less in the obese prolactin ‘non-responder’ women supports the hypothesis for a hypothalamic disorder.