1. Endogenous digoxin-like immunoreactivity (EDLI) was measured in the serum of 85 normotensive pregnant (NTP) women and 77 women with pregnancy-induced hypertension (PIH) by a radioimmunoassay (New England Nuclear). All women were in the third trimester.
2. EDLI, which was undetectable in serum from nonpregnant women, was present in NTP and PIH and was significantly higher in PIH. EDLI correlated with gestational age in NTP, but not in PIH.
3. Ouabain-sensitive Na+ transport was estimated in normal peripheral blood leucocytes after incubation with sera from 50 NTP and 42 PIH women. Significant inhibition of active Na+ transport occurred only with the serum of hypertensive patients without proteinuria.
4. EDLI did not correlate with the effect of the sera on active Na+ transport. The radioimmunoassay therefore provides a poor index of Na+ transport inhibitory activity in PIH.