Subcortical electrical stimulation was applied to the prospective surgical target area during 158 stereotactic operations in 135 psychiatric patients. The following target areas were studied: rostral cingulum below and in front of the genu of the corpus callosum (52 cases) genu (46) cingululum just above the genu (11) middle cingulum (6) anterior internal capsule (33) subcaudate region, 'substantia innominata' (10 cases). Forty-seven per cent of the cases reacted to stimulation with subjective emotional sensory responses. Stimulation of differ targets had significantly different results. Responses were obtained most frequently from the cingulum and genu, and least frequently from the anterior capsule and subcaudate regions. Stimulation of the rostral cingulum often caused 'negative' responses, i.e. an increase in or the appearance of anxiety and tension (11/15 cases). The opposite was true of the adjacent genu of the corpus callosum; on stimulation of this structure anxiety and tension disappeared or diminished (18/19 cases). Schizophrenic patients experienced such 'positive' responses significantly more often than non-schizophrenics. In non-anesthetized patients autonomic reactions were very rare.