The role of nitric oxide (NO) in mediating pancreatic endocrine responses to moderate hypoglycaemia has been investigated in conscious unrestrained calves. The synthesis of endogenous NO was inhibited by the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mg kg-1 I.A.), while sodium nitroprusside was infused continuously (2-4 μg min-1 kg-1 I.V.) to mimic the tonic production of NO. This effectively abolished the rise in plasma pancreatic polypeptide (PP) concentration during moderate hypoglycaemia (0·7 nmol kg-1 insulin I.V.) and significantly reduced the response to more intense hypoglycaemia (2·0 nmol kg-1 insulin I.V.). In contrast, the glucagon response was not significantly affected in either group, although consistently higher plasma glucagon values were obtained in response to the higher dose of insulin following the administration of L-NAME. It is concluded that, in the absence of L-NAME, production of NO contributes to the PP response, but not the glucagon response to hypoglycaemia in this species under physiological conditions.