Eyeblink classical conditioning (EBCC) is severely and consistently impaired in probable Alzheimer's disease (AD), presumably due to normal age related changes in the cerebellum and AD-related hippocampal cholinergic disruption. Less consistent impairment and more variable EBCC performance was predicted in patients with cerebrovascular dementia (CVD) because some CVD patients should have impairment in EBCC when their lesions affect the EBCC circuitry, whereas others with lesions in noncritical regions should have normal EBCC. As predicted, variability in EBCC performance was greater in patients with CVD than in probable AD patients. Acquisition of conditioned responses in the group of CVD patients was better than in the probable AD group. These data show in another sample of normal control subjects and probable AD patients that EBCC has a high sensitivity for probable AD.