OBJECTIVE--To examine mechanisms controlling the stapedial reflex in patients with amyotrophic sclerosis (ALS). METHODS--The stapedial reflex was examined using impedance audiometry in 38 patients with sporadic ALS and in 25 age matched controls. RESULTS--All patients showed normal reflex decay test results. There were no significant differences between patients with ALS and control subjects in reflex threshold, latency, amplitude, or contraction time (C50). Although each reflex variable in the patients with classic or progressive muscular atrophy types of ALS showed no significant difference from that in control subjects, the patients with bulbar type ALS showed significantly longer latency, C50, and retraction time (D50), and significantly lower amplitude than control subjects. Three types of abnormal reflex waveforms (polyphasic, abnormally delayed retraction, and abnormally early retraction) were noted in six patients. CONCLUSION--The subclinical involvement of the stapedius motor neurons or of the supranuclear stapedius motor system might be responsible for the abnormalities of the stapedial reflex in ALS.