The aim of the study was to analyse the diagnostic value of blink reflex (BR) in motor neuron disease (MND). We studied 25 patients with MND including amyotrophic lateral sclerosis (ALS) in 18 patients, primary muscular atrophy (PMA) in 4 patients, and primary lateral sclerosis (PLS) in 3 patients and 12 healthy volunteers. The blink reflex was obtained in typical way. In ALS group, statistically significant increase in latency and decreased amplitude of R2 responses were found compared to the control group (p < 0.05), whereas BR in patients with PLS and PMA was within normal limits. The presence of low amplitude of R2 responses in patients with ALS may suggest loss of lower brainstem neurons connecting trigeminal and facial system, and probably also decreased facilitator effect of central nervous system on reticular formation in the brainstem.