Early in gestation maternal blood volume normally expands by an unknown mechanism; failure of this normal adaptation to pregnancy has been associated with common adverse pregnancy outcomes including preeclampsia, intrauterine growth retardation, and premature labor. The renin-angiotensin system has a critical role in controlling maternal fluid volume and probably in the pathophysiology of these serious complications of pregnancy. Kenneth Ward and his group have recently discovered DNA variants which cause amino acid substitutions in angiotensinogen (renin substrate), one of which (T235) is strongly associated with preeclampsia. They hypothesize that functionally different angiotensinogen proteins may underlie the pathophysiology of preeclampsia and other related disorders (such as intrauterine growth retardation and premature labor) by not allowing normal volume expansion to occur.