Knowledge of the neural circuits involved in Wallenberg's syndrome (WS) is incomplete. Study of the blink reflex (BR) in patients with WS can help in reaching a better understanding of the physiopathology underlying clinical symptoms and may help in the prediction of clinical outcome. We evaluated the BR in response to supraorbital nerve electrical stimuli in 20 patients with WS. All patients were studied within the 1st week after onset of symptoms, and 10 of them were also studied repeatedly during a follow-up period of 3-12 months. At the first examination the long latency bilateral responses (R2 and R2c) to stimulation of the supraorbital nerve of the affected side were absent in 11, delayed in 4, and normal in 5 patients. At follow-up, there was a normalization of the BR in all patients who had absent or delayed responses at the first examination except for one patient whose responses remained absent at the 9th month. Late responses elicited on the side of the lesion by stimulation of the non-affected supraorbital nerve were normal in all but one patient. This patient died from cardiorespiratory arrest within the 1st month of the illness. One patient with normal BR responses also died in the acute phase. The BR is abnormal in most patients with acute WS and tends to normalize in a mean period of 7 months. BR pattern is not a predictor of early fatal complications in patients with this syndrome.