Abstract
SUMMARY: 1. Samples of plasma and serum from healthy non-pregnant women, from normal gravidae and from patients with pre-eclamptic toxaemia have been tested for antidiuretic activity by means of the method described by Jeffers, Livezey & Austin [1942]. 2. An antidiuretic substance (ADS) is present in normal pregnancy serum, and in pre-eclamptic plasma and serum. ADS was not detected in non-pregnant serum or plasma or in normal pregnancy plasma. 3. Normal pregnancy plasma contains a substance which inactivates both vasopressin and the ADS present in normal pregnancy serum and in pre-eclamptic plasma. This inactivator was not demonstrated in non-pregnant plasma. 4. Vasopressin and ADS are inactivated both by thioglycollic acid and normal pregnancy plasma. 5. The antidiuretic activity of normal pregnancy serum is not attributable to 5-hydroxytryptamine (5-HT).