After exposure to a prolonged tone of changing intensity but constant frequency, controls, patients with peripheral hearing loss, and patients with multiple sclerosis (MS) demonstrated a reduced sensitivity to shifts in intensity; sensitivity to frequency shifts was unaffected. After exposure to a prolonged tone of changing frequency but constant intensity, control and patients with peripheral hearing loss demonstrated reduced sensitivity to shifts in frequency; sensitivity to intensity shifts was unaffected. Some patients with MS showed no loss of sensitivity to shifts in frequency. Our findings suggest that some patients with MS have abnormal mechanisms for processing changes of frequency. If such processing of frequency change is important for understanding speech, then this observation of a specific central hearing defect may help to explain poor speech discrimination in some patients with MS who have normal audiograms.