Although patients with multi-infarct dementia (MID) may have greater spontaneity than those with dementia of the Alzheimer's type (DAT), conventional neuropsychological tests often fail to distinguish between these two dementias. We studied 18 patients with MID and compared them to 18 comparably demented patients with DAT and 18 normal elderly controls on conventional structured tests and two unstructured tasks, a 3-minute verbal description of the Cookie Theft Picture and the Lezak Tinker Toy Test. On the structured tests, the only significant difference between the two dementia groups was worse performance by the DAT patients on several memory measures. On the unstructured tasks, the MID group had significantly fewer words/minute and constructional assemblages. These results suggest that unstructured tasks help distinguish patients with MID from those with DAT, and that MID patients have decreased spontaneous behavior and initiation, possibly reflecting frontal-subcortical pathology and compromised executive abilities.