Normal pregnancy is associated with refractoriness to the pressor effects of i.v. administered angiotensin II (A II). In pre-eclampsia, this refractoriness to A II is lost several weeks prior to the increase of blood pressure. Infusions of 200 ml of 3% saline or of 40% sorbitol over 30 min, or administration of 2,000 ml of normal saline infused over 2 h, respectively, resulted in an increased vascular angiotensin sensitivity. The effective angiotensin pressor dose (APD) decreased significantly after each test substance (decrease of the mean APD 14.5% after 3% saline, 24% after 40% sorbitol and 25% after normal saline). The data confirm the hypothesis that the principal determinant of pressor responsiveness to A II during pregnancy is arteriolar response; this seems to be modulated by alterations in the sodium content of the vessel wall.