The pathophysiology of oromandibular dystonia is being studied to determine whether movement abnormalities are due to hypertonia in some muscles or a lack of normal activation of opposing muscles, which might explain the poor responses of some patients to injection with botulinum toxin. In addition, the alterations of muscle activation patterns are being compared across tasks to determine whether muscle activation abnormalities differ between chewing and speech in these patients. The effects of fluency enhancing conditions (DAF, choral reading, white noise) on speech production in stutterers were compared with normal speakers' changes. In normal controls, the only common change across conditions was an increase in vowel duration. This change was not found in the stutterers, although decreases in peak airflow were related to increases in fluency across each of the conditions in the stutterers. An open trial study of the effects of botulinum toxin injections in the laryngeal and oral muscles was completed in 10 stutterers this year. There were significant reductions in the percent of time dysfluency occurred in 8 of the 10 subjects following unilateral thyroarytenoid injections. No improvement in fluency occurred following bilateral injections of following lip or jaw injections. We are currently conducting double line cross-over studies of the effects of botulinum toxin on fluency and comparing the effects of clomipramine and desipramine on stuttering in collaboration with the Child Psychiatry Branch, NIMH.