The purpose is to determine the relationship between impairments in speech production and language in patients with different neurological diseases. The degree of language impairment and the relationship between deficits in speech production, language processing, and speech perception in various forms of neurological diseases in unclear. The speech problems of patients with dysarthria associated with Parkinson's disease have previously been thought to be neuromotor. Recent results have indicated that these patients may also have language encoding and decoding difficulties which could further confound their neuromotor difficulties. Three studies are ongoing. The results of testing language encoding and decoding in patients with Parkinson's disease are being examined for relation-ship with several other characteristics such as duration of disease, side of involvement, drug treatment and speech impairment. Auditory processing and speech perception studies are ongoing in patients with Huntington's disease. Finally, a unique case of auditory agnosia was studied and found to exhibit normal peripheral hearing with no volitional response to sound and intact phonological coding. This case demonstrated the independence of phonological decoding from auditory perception.