Recently, several cases of pure agraphia caused by left parietal lobe lesion have been reported. Most of the reported cases were caused by space-occupying lesions, but clinical descriptions and anatomical correlations were not sufficiently detailed.     The present authors investigated two cases of pure agraphia caused by left posterior parietal infarction. Detailed analyses of symptoms, CT scans and ¹³NH₃ PET (Positron Emission Tomography) were performed.     The characteristics of the symptoms in both cases were : 1) Agraphia was present with both hands. 2) Copying was not greatly disturbed as compared with spontaneous writing or dictation. 3) Agraphia was characterized mainly by paragraphia, non-reaction, omissions and wrong writing order of letters. 4) One patient who had much knowledge of English was examined as to his writing and oral spelling in English.     The main lesions in the CT scan were found in the left supramarginal gyrus and the upper parietal lobe. The functional lesions seen in ¹³NH₃ PET were much wider than those in CT scan but not extending to the frontal lobe. These observations suggest that pure agraphia may also be caused by left parietal lobe lesion.