The present study was undertaken to investigate the effect of osmotic constituents of the incubation media on angiotensin II stimulation of arginine vasopressin (AVP) release from the organ-cultured guinea pig hypothalamo-neurohypophyseal complex (HNC). As reported previously, the addition of angiotensin II caused a significant increase in AVP release from the explants of HNC incubating in the normal culture medium. The media made hyperosmolar with sodium chloride also significantly increased AVP release from the explants. The addition of angiotensin II to the hyperosmolar sodium chloride caused a further increase in AVP release from the explants of HNC. However, the response to angiotensin II was not significantly different among the explants incubating in the hyposmolar, the isosmolar and the hyperosmolar sodium chloride solutions, indicating separate pathways of angiotensin II and osmotic stimuli in AVP release. In contrast, the response of the explants to angiotensin II was markedly suppressed when they were incubated in the media made hyperosmolar with excess glucose. Furthermore, the hyperosmolar media of excess urea failed to influence the angiotensin II-stimulated AVP release from the explants. These results are compatible with the hypothesis that excess glucose has a specific suppressive effect on AVP release from the neurohypophysis.