Microinjections of the neuroexcitatory substance l-glutamate, were made directly into various laminae of trigeminal nucleus caudalis to examine the influence of medullary dorsal horn neurons on the adrenal secretion of catecholamines in the anesthetized cat. Microinjections into the marginal layers (lamina I-II) or into the deep magnocellular portion (lamina V-VI) of nucleus caudalis ipsilateral to the adrenal vein sample evoked a prompt increase in the secretion of epinephrine and a smaller, yet consistent, increase in the secretion of norepinephrine. Injections into the magnocellular layers (lamina III-IV) had no significant effect on secretion of catecholamines. Injections into nucleus caudalis, contralateral to the adrenal vein sample, had no consistent effect on secretion suggesting that the central pathway from nucleus caudalis to the spinal cord for control of adrenal secretion of catecholamines is mainly ipsilateral. Changes in the adrenal secretion of epinephrine were not correlated with changes in adrenal venous blood flow, in arterial pressure or in heart rate. Arterial pressure was transiently increased by l-glutamate injections into the marginal layers, whereas injections into other laminae had no consistent effect. Heart rate increased regardless of the laminar site injection. The results indicate that local excitation of nucleus caudalis, in laminae that contain the majority of nociceptive neurons, evokes a consistent increase in the adrenal secretion of catecholamines, whereas excitation of neurons in laminae that mainly process non-noxious sensory input has no significant effect. It is concluded that secondary trigeminal neurons that contribute to the autonomie responses to noxious trigeminal stimuli have a similar distribution within nucleus caudalis as those that underlie the sensory-discriminative aspects of nociceptive.