Behavior modification as an attack upon the problem of mutism in mongoloid children establishes the basis of the text. Case histories of four children in a state institution present the specific strategy of speech therapy using verbal conditioning. Imitation and attending behavior, verbal chaining, phonetic theory, social reinforcement, deprivation, and punishment are all examined in relation to the four subjects. The etiology of mutism among institutionalized mongoloid children is dealt with in a separate section. A glossary of phonetic symbols and terminology conclude the text. (CD)