Complications of the gastrointestinal tract in patients with diabetes mellitus can cause marked discomfort and may modify the ability of the patient to maintain normal glucostasis. In an attempt to elucidate some of the factors causing gastrointestinal dysfunction in experimental diabetes we examined the responses of jejunal smooth muscle in streptozotocin-induced diabetes in rats to some of the neurotransmitters and autocoids found in the enteric nervous system. Jejunal tissues from 4- to 5-week diabetic rats were examined for their responses to neurokinin (NK) A, NKB, substance P (SP), bradykinin, neurotensin, bethanechol, isoproterenol and phenylephrine. The affinities for all these agonists, except for SP which increased slightly with diabetes, were the same in both control and diabetic tissues. NKA was the most potent neurokinin and elicited the largest contractile responses from jejunal tissues of both control and diabetic animals. The contractile response to NKA, but not that to NKB or SP, was increased in the jejunum from diabetic animals. Part of this increased responsiveness was antagonized by atropine. The contractile effects of the cholinergic agonist, bethanechol, were not altered by the diabetic state. Decreased relaxation responses in the jejunum from diabetic animals were observed for bradykinin, neurotensin and isoproterenol, but not for phenylephrine. These results suggest that the myogenic actions of several agonists are modified in experimental diabetes.