The authors assessed alpha-adrenergic receptor function in blood platelets from chronic schizophrenic patients and normal control subjects. The number of receptors was measured by the specific binding of the alpha-adrenergic antagonist [3H]dihydroergocryptine to the platelets. A physiological response of the platelets to agonist occupancy of the alpha-adrenergic receptors was measured by the norepinephrine inhibition of prostaglandin E1(PGE1)-stimulated cyclic AMP (cAMP) production. cAMP production in male schizophrenic patients was lower than in normal male subjects. alpha-Adrenergic receptor function was similar in patients and normal control subjects of both sexes. Normal male subjects had about 1.5 times the number of alpha-adrenergic receptors as normal females and generated about 1.8 times the quantity of PGE1-stimulated cAMP.