The relevance of movement disorders to neuropsychiatric illness has become increasingly apparent with the discovery that symptoms of Parkinson's disease may occur as side effects during therapeutic administration of neuroleptic drugs and that cessation of neuroleptics may be followed by tardive dyskinesia. The potential value of information concerning such neurochemically determined motor disorders is twofold: 1) at an applied level, quantitative measures of motor function will be useful in drug regulation of therapeutic agents and in drug effectiveness comparisons for different agents; 2) at a basic level, discovery of mechanisms of motor disorders will help us to understand the brain disturbances underlying the wide range of neuropsychiatric illnesses related to neurochemical disturbances. Studies thus far have focused on obtaining quantitative indices of the fluctuations in effectiveness of anti-parkinsonian drug therapy. Tests of movement speed and reflex responses to limb displacement have provided us with measures which correlate with clinically determined fluctuations in drug efficacy, pointing to the feasibility of setting up routine tests of motor function to be administered in clinical settings.