Intrusive or perseverative errors as evidenced on tests of memory have been found to occur with greater frequency in patients with Alzheimer's Disease (AD) relative to other disorders and are thought to reflect the cholinergic deficits associated with AD. A particular type of intrusive error, semantic intrusions, has been found to discriminate AD from multi-infarct dementia and normal elderly controls. However, it has been suggested that such errors actually reflect random responding as the result of the disinhibition often observed in AD patients. The present study compared the frequency and types of intrusive errors from a sample of mildly, moderately, and more severely impaired AD patients who had undergone the Fuld Object Memory Evaluation with the "guesses" of elderly controls. Results of this study indicate that the semantic intrusions of AD patients differ both in type and frequency from the guesses of the control subjects.