The increase in blood insulin level induced by adrenergic beta-stimulants, glucose and tolbutamide was strongly exaggerated in pertussis-sensitized rats. Moreover, the decrease in blood insulin caused by the alpha-receptor-mediated action of epinephrine in glucose- or tolbutamide-treated rats was effectively reversed by pertussis sensitization. The rise of blood insulin concentration due to adrenergic alpha-blockade was also enhanced by pertussis sensitization. It is concluded that the secretion of insulin resulting from the stimulation of adrenergic bate-receptor is enhanced by pertussis sensitization, probably due to activation of a process occurring in the chain of events leading to the discharge of insulin from the pancreatic beta-cell.