OBJECTIVE The object of the present study is to show the spectrum of neurophysiological findings during clinical course of Miller Fisher syndrome (MFS), avoiding the controversy over a combined central and peripheral pathology. PATIENTS AND METHODS We report five patients with a syndrome of ophthalmoplegia, ataxia and areflexia. A similar episode had been suffered previously by 2 of these patients, 14 and 13 years before. In one of them the second episode evolved to a typical Guillain-Barré syndrome (GBS). Motor and sensory conduction velocity of upper and lower limbs, F waves, blink-reflex and somatosensory evoked potentials were recorded in all cases. Needle electromyography in four and brainstem evoked potentials in three of them and the jaw-reflex in another one. RESULTS In all patients there was a markedly reduced amplitude of the distal sensory evoked response, and no signs of denervation in the EMG. The other results were variable both interindividually and intraindividually. The severity of abnormalities was also different between different patients. The clinical recovery was always accompanied by a improvement of neurophysiological parameters. CONCLUSIONS The electrophysiological findings in MFS can be variable but they appear always related with the clinical symptomatology. We report for the first time a case in whom the jaw-reflex was abnormal whereas the blink-reflex was normal.