We have recently proposed that the cognitive deficits of patients with multiple sclerosis (MS) share numerous characteristics associated with the syndrome of subcortical dementia. One such characteristic, slowness of mental processing, was evaluated in the present study. Thirty-six MS patients were compared to 26 normal controls of equivalent age, education, and verbal intelligence on the Sternberg memory scanning test. As anticipated, the motor-involved MS patients had an overall slower reaction time than did controls. Their scanning rate, a measure of pure cognitive speed, was also significantly slower than controls. These results suggest that MS patients exhibit a slowing of mental processing independent of motor involvement.