Two writing routes (phonological and lexical) have been postulated. We studied four patients who had disruption of the phonological route (ie, inability to write pronounceable nonwords) but with a preserved lexical route. Results showed that the phonological route has two components: segmentation and phoneme-grapheme conversion. Disruption of either function may induce phonological agraphia. The preserved lexical route uses a whole-word mechanism and is strongly affected by semantic factors, such as imageability, emotionality, and grammatic class. Results of CT suggest that a portion of the supramarginal gyrus is the most likely anatomic substrate of phonological agraphia. © 1983 American Academy of Neurology.