Dopamine receptors in intracerebral motor and endocrine systems have been divided into two main types, D-1 and D-2, dependent on the presence or absence of adenylate cyclase linkage. Here we have investigated a number of dopamine agonist and antagonist drugs in man that have different actions on D-1 and D-2 receptors in animals. Motor and endocrine effects in parkinsonian subjects seem to depend on drug interaction with D-2, but not D-1, receptors. These results may have important implications for the design of anti-parkinsonian and antipsychotic agents.