The major site of pathology in Huntington''s chorea is the striatum. The neurons of the striatum degenerate but the striatal content of dopamine remains normal. It is proposed that abnormally heightened responsiveness on the part of striatal receptors to dopamine underlies the initiation of chorea. This concept is supported by results with a variety of agents including rauwolfia alkaloids, phenothiazines, butyrophenones, and alphamethyl-p-tyrosine. An analogous heightened responsiveness to serotonin explain the aggravation of chorea by 5-hydroxytryptophan. An overall deqreased responsiveness to dopamine may be related to the development of rigidity in this disease. It is suggested that L-dopa and 5-hydroxytrytophan may be of value to detecting the presymptomatic individual.