Twenty-four patients with Guillain-Barré syndrome were prospectively evaluated for evidence of autonomic dysfunction. It occurred in 16 (66.7%) patients, usually during the peak period of paralysis, in the form of either excess or inadequate activity of sympathetic and/or parasympathetic nervous systems. Its clinical manifestations comprised of sinus tachycardia (33.3%), bradycardia (8.3%), hypertension (33.3%), postural hypotension (35%), urinary sphincteric disturbances (20.8%) and anhydrosis of lower limbs (12.5%). Assessment of cardiovascular responses to autonomic function tests revealed impaired alterations in heart rate during deep breathing (31.6%), Valsalva's manoeuvre (28.6%), sustained handgrip (25%), cold-pressor test (36.4%), postural change (35%) and atropine test (20%); and impaired rise in blood pressure during firm handgrip (25%) and cold-pressor test (36.6%). ECG abnormalities were noticed in 8 (33.3%) patients. They comprised of depressed ST segment in 5, inverted T wave in 3, tall T wave in 2 and prolonged QTc in 2 patients. Two patients died of respiratory failure. Autonomic dysfunction in Guillain-Barré syndrome did not appear to have any prognostic significance as there was no significant difference in autonomic dysfunction between good - and bad - outcome groups of patients.