The study of the nature and the role of epinephrine containing neuron in brain has been continued. A previously reported finding that phenylethanolamine N-Methyl transferase (PNMT) was higher than normal in spontaneously hypertensive rats was confirmed. Immunohistochemical analysis indicated that this increased activity was associated with an increase number of neurons rather than an increased activity per cell. We have also found that the brain PNMT activity can be enhanced by dexamethasone or a stressful situation. This increase in activity occurs over a short time course and suggest activation of preformed enzyme molecules. In related experiments we observed the effect of unilateral carotid artery ligation. Of interest was the relatively rapid increase (40%) in PNMT activity on the contralateral side of the brain.