Slowly progressive aphasia: three cases with language, memory, CT and PET data. Three cases of slowly progressive speech and language disturbance were studied at various points post onset (three, five and 15 years respectively). Language, neuropsychological and brain imaging (computer tomography and positron emission tomography) evaluations were completed on all three patients. The data suggest that the syndrome of "progressive aphasia": 1) does not involve a uniform symptom complex; 2) does not necessarily develop into a full blown dementia syndrome; 3) varies greatly in rate of progression from case to case; 4) is associated with normal brain structure (on computer tomography); and 5) is associated with abnormal left temporal lobe metabolism as measured by fluorodeoxyglucose (FDG) positron emission tomography (PET). One patient had histological findings consistent with Alzheimer's disease at necropsy. 