Testing of the autonomic cardiovascular reflexes (single breath beat-to-beat variation and orthostatic blood pressure change) was performed in 542 patients with erectile dysfunction who were grouped according to aetiological factors and their response to visual sexual stimulation and the papaverine test. Age-related normal values for autonomic tests were determined in the group of 124 patients with psychogenic impotence. Abnormal cardiovascular reflexes were associated with ageing and organic impotence, indicating autonomic dysfunction as a major contribution to impotence. Single breath beat-to-beat variation, as a simple non-invasive test, is useful in the clinical evaluation of impotence, especially in patients with diabetes and a history of alcohol abuse.