The distribution of nitricoxideergic neurons and activity of neuronal NO-synthase (nNOS) was studied in some nuclei of the medulla oblongata in patients with the lifetime diagnosis of arterial hypertension, stages I-III (AG I-III). In AG I, the significant decrease of nNOS activity was observed in most nuclei, although the relative content of NO-neurons was not changed. The marked changes of these parameters were noted in the nucleus of solitary tract compared to those of the reticular formation. In AG II, a portion NO-neurons in the nuclei was markedly reduced, however the following decrease of nNOS activity was not found. In AG III, there was the augmentation of nNOS activity and the subtle decrease in the portion of NO-neurons. Therefore, in AG, there is the decrease of quantitative parameters that characterize the state of the oxide-ergic system. This is one of the causes of the hyperactivation of sympathetic nervous system and elevation of arterial pressure. The exception is the dorsal nucleus of the vagus nerve, in which the relatively larger number of NO-neurons and higher nNOS activity were found, that may be related with the cholinergic mechanism of compensatory activation of the nitric oxide-ergic system.