Serial estimation of plasma nor-epinephrine (PNE), 24 hours urinary vanilmandelic acid (VMA) and plasma cortisol was made in 25 adult patients of Guillain-Barré syndrome. Healthy adult age and sex matched volunteers served as controls. The mean level of PNE, VMA and plasma cortisol in controls was 1.07 +/- 0.50 ng/ml, 2.81 +/- 1.18 mg/24 hours and 12.9 +/- 3.10 micrograms/100 ml, respectively. In cases of Guillain-Barré syndrome with autonomic dysfunction the mean level of PNE, VMA and plasma cortisol was 3.34 +/- 2.47 ng/ml, 7.98 +/- 5.71 mg/24 hours and 27.25 +/- 4.94 micrograms/100 ml on the day of admission while in cases of Guillain-Barré syndrome without autonomic dysfunction it was 1.09 +/- 0.32 ng/ml, 3.04 +/- 2.22 mg/24 hours and 11.8 +/- 4.2 micrograms/100 ml, respectively. An increase in circulating PNE, VMA and plasma cortisol was demonstrated in patients of Guillain-Barré syndrome with autonomic dysfunction presenting as hypertension and tachycardia. The maximum rise of 284% (PNE) and 253% (VMA) occurred at the height of paralysis. The elevated levels fell to near control values at the time of significant recovery, and glucose tolerance tests improved. It is suggested that increased levels of catecholamines and cortisol contributed to the development of dysautonomia as these levels were within normal limits in patients of Guillain-Barré syndrome without autonomic dysfunction.