Autonomic neuropathies are a frequent complication to diabetes in humans. Similar neuropathies have not been well-documented in animal models. To determine if diabetic rats would develop parasympathetic neuropathies, rats were made diabetic by the injection of alloxan into the tail vein and then maintained on daily injections of insulin. At various times subsequent to the induction of diabetes (3-5 weeks, 7-9 weeks, and 14 weeks), the effect of constant frequencies of vagal stimulation on the efferent cardiac chronotropic response was evaluated using analysis of variance techniques. It was found that the vagal parasympathetic effect was accentuated in diabetic rats. That is, at a given frequency of supramaximal vagal stimulation, the heart rate slowed more in diabetic rats than in nondiabetic rats. Whether a similar phenomenon exists in humans is not known.