This paper shows the basic and clinical evaluations of pressor responsiveness to angiotensin II (A II) using A II sensitivity test (AST) in normotensive and hypertensive pregnant women. The results are as follows: I. Basic findings of A II pressor responsiveness 1. AST was performed sequentially from as early in gestation as possible throughout the remainder of pregnancy. At clinic visit the patients received A II infusions sufficient to raise baseline diastolic blood pressure by 20 mmHg. The dose (ng/kg/min) of A II required to elevate 20 mmHg of diastolic blood pressure was recorded as the EPD. Increased EPD indicates the dullness of refractoriness to A II. The EPD in normotensive women (non-PIH) increased as early as midpregnancy, but EPD in women destined to develop pregnancy-induced-hypertension (PIH) decreased significantly after the 20th week of gestation. 2. Plasma angiotensin level in non-PIH increased significantly compared to that of PIH. There exists a definite correlation between EPD in pregnant women and plasma angiotensin level. 3. The plasma TxB2/6-keto-PGF1 alpha ratio increased significantly in PIH compared with that of non-PIH because of the increase in the amount of TxB2. In the 2nd trimester, the ratio in women destined to developed PIH showed a significantly higher value than that of the non-PIH. 4. In healthy men and castrated rats the EPD significantly increased after the administration of progesterone. At 20 and 30 weeks' gestation, the plasma progesterone/estrogen ratio in women destined to develop PIH decreased significantly compared to that of the non-PIH.(ABSTRACT TRUNCATED AT 250 WORDS)