We present two cases of primary progressive aphasia studied with neuropsychologic measures, computed tomography or magnetic resonance imaging, and single-photon emission computed tomography with technetium Tc99m-labeled hexamethylpropyleneamine oxime. Clinical and neuropsychologic observations revealed a marked, progressive loss of language functions over time with relative preservation of nonlanguage cognitive functions in both patients. The brain single-photon emission computed tomographic scan revealed marked left frontal and minimal left temporal and parietal hypoperfusion in case 1 and marked left posterior frontal and minimal left temporal hypoperfusion in case 2. The value of brain single-photon emission computed tomography in distinguishing primary progressive aphasia from Alzheimer's disease is described.