The influence of glucose administration on plasma cortisol level after its elevation by pharmacological and physiological interventions in healthy male volunteers was studied. The increase of plasma cortisol after 1 g of L-dihydroxyphenylalanine (L-dopa) failed to be significant. However, after a concomitant oral administration of 100 g glucose, a fall of cortisol level significant also vs. initial control values was observed. The infusion of beta adrenergic blocking agent (propranolol) enhanced the cortisol response to physical exercise. However, the glucose given before propranolol infusion abolished the enhancement of cortisol response induced by this drug. The mechanism of the inhibitory effects of glucose remains to be elucidated.