To study the neurophysiological mechanisms of neurasthenia, hysterical neurosis and obsession neurosis with a view to the practical employment of the results, the authors examined 100 patients and 40 normal subjects using the method of evoked potentials (EP). EP changes indicated an neurasthenia-related decrease in the functional activity of the cortex, weakening of its inhibitive functions and an increase in the reactivity of the system of negative-emotional support. Patients with hysterical neurosis displayed the greatest excitability of the structures of the projective pathways and insufficiency of programme-integrating effects of the higher portions of the brain. Neurosis of obsessive states was characterized by an increase in the activity of specific cortical zones and, to a larger degree, of the centres of negative-emotional reactivity. The time-course of EP during treatment is outlined. The findings obtained may serve as additional criteria in the diagnosis and treatment of neurosis.