Patients with Huntington's Chorea and alcholic Korsakoff's disease were compared on six tests of short-term memory (STM) and of encoding capacity. While the alcoholic Korsakoff patients demonstrated STM disorders related to an increase sensitivity to proactive interference (PI) and to failures in semantic encoding, the Chorea patients had a different pattern of deficits. The Chorea patients, like the Korsakoffs, had STM deficits, but their memory performance did not improve with reductions in PI, and they had different types of encoding deficits than did the Korsakoff patients. These results demonstrate that information processing tasks can be used to empirically differentiate amnesic patients with normal I.Q.'s from patients with dementia-related memory impairments.