We compared 13 patients with dementia of the Alzheimer's type (DAT) and 9 progressive supranuclear palsy (PSP) patients, matched by age, sex, education, and the overall level of cognitive deterioration, measured by using the Dementia Rating Scale, and 12 normal controls. The results of this study confirm that the pattern of cognitive deterioration of PSP patients differs from that of DAT patients. While episodic memory is severely affected early in the course of DAT, it appears to be relatively spared in PSP. In contrast to previous suggestions, we found no evidence for differentially rapid forgetting in DAT, although we did confirm relatively preserved recognition memory in PSP. We had predicted that the performance of the DAT group on tests of semantic memory (the Boston Naming Test, the ADA Synonym Judgement Test, and the Pyramids and Palm Trees Test) would be worse than that of the PSP group. However, there was, in fact, no difference on any of these measures, except that the PSP patients showed a significantly greater deficit on the Synonym Judgement Test. We suggest that the underlying cause of the semantic memory impairment might, however, be different in the two pathologies.