The prolactin (PRL) response to 20 mg of domperidone, a peripheral dopamine (DA) blocking agent, was evaluated in a group of 16 drug-free, acute, young schizophreniform and schizophrenic males and in a group of age-matched normal males. Although basal plasma PRL levels were normal, the PRL responses following domperidone were blunted in both patient groups. The PRL response was more blunted in the schizophreniform patients than in the schizophrenic patients. Possible explanations for these results include pharmacokinetic factors or abnormalities of the pituitary D2 DA receptors.