We investigated the brainstem blink reflex in patients suffering from idiopathic and symptomatic trigeminal neuralgia to establish possible dysfunction in the reflex cycle and determine eventual differences between the two disease types. The study included 35 patients with idiopathic disease and seven patients with symptomatic disease, their results compared with those of 50 normal controls. We stimulated the forehead afferents of the supraorbital nerve and recorded the response from both orbicularis oculi muscles. We tested latencies of bilateral late components (R2, R2'), irritative R3 component and the incidence of R3 component. The patients with idiopathic trigeminal neuralgia showed normal parameters of blink reflex, except for the greater incidence of R3 component. Patients with symptomatic trigeminal neuralgia showed prolonged latencies of R2, R2' and R3 components when stimulating the afflicted side, but no significant difference in incidence of R3 component compared with the control group. The results indicate that abnormalities of blink reflex are significantly different in the two groups of patients. The high incidence of R3 component seems to be typical of idiopathic disease, whereas the prolonged latencies of late reflex components after stimulation of the afflicted side seem to be typical for symptomatic disease. These results suggest that testing the blink reflex may prove a significant aid in distinguishing the idiopathic and symptomatic disease types.