To clarify the impact of autonomic neuropathy in diabetic patients, we have conducted a prospective study of 58 Type 1 and 51 Type 2 diabetic patients (investigated at baseline, after 4, and after 7 years). In Type 1 diabetic patients, the sympathetic nerve function (orthostatic acceleration and brake indices) and in Type 2 patients, parasympathetic nerve function (R-R interval variation; E/l ratio) deteriorated during 7 years of prospective observation. Symptoms of autonomic neuropathy were associated with signs of autonomic neuropathy (low brake indices) in Type 1 but not in Type 2 diabetic patients. In the latest assessment 24 h ECG recording was performed and blood samples assayed for neuropeptide Y (NPY) and motilin were obtained. Type 1 diabetic patients with parasympathetic neuropathy (abnormal E/l ratio) showed significantly lower SD value (less variation in the R-R intervals; 29 [17] vs 50 [16], [mean (interquartile range)]; p = 0.001) and higher postprandial plasma motilin values (70 [20] pmol l-1 vs 50 [15] pmol l-1; p < 0.01) than patients with normal parasympathetic nerve function. In Type 2 diabetic patients, sympathetic neuropathy (low brake indices) was associated with an increased frequency of ventricular extra systolic beats during 24 h ECG recording (rs = 0.65; p < 0.01). Postprandial plasma NPY levels were not associated with disturbed autonomic nerve function.