This study investigated the speed of short-term memory scanning in two groups of patients: patients with Parkinson's disease (PD) (primarily subcortical pathology) and patients with a presumptive diagnosis of dementia of the Alzheimer type (DAT) (primarily cortical pathology). Non-demented PD patients (M age = 58.3), mildly demented DAT patients (M age = 67.0), and normal control (NC) subjects (M age = 58.9) were compared to one another in order to determine whether the presence of slowed scanning differentiates subcortical from cortical pathology. The three groups did not differ significantly on the memory scanning task. Slowed scanning speed does appear to occur in some patients with PD, however. This may relate to age, duration of disease, or an interaction between these two. Despite normal scanning speed, most DAT patients required highly structured instructions to be able to carry out the item-recognition task, and many remainedunable to perform this task even with additional instructions.