The association between treatment with danazol and hyperglucagonaemia was studied. Plasma glucagon concentrations were measured during an oral glucose tolerance test in seven women taking danazol and six healthy controls not taking danazol. Results showed that treatment with danazol is associated with severe hyperglucagonaemia, and in three patients glucagon concentrations reached the range suggestive of glucagonoma. It is important to recognise that this increasingly used drug may cause severe hyperglucagonaemia to prevent patients treated with danazol undergoing unnecessary investigations to localise glucagonoma.