Disorders associated with hypertension during pregnancy, which are often linked with edema and/or proteinuria and are variously termed toxemia of pregnancy, EPH [edema, proteinuria and hypertension] gestosis, preeclampsia and eclampsia, are of unknown etiology, although they have been known for a long time and many attempts have been made to classify and explain them. The problems of standardizing values for blood pressure, proteinuria and edema, and of determining their value in the diagnosis of the disorder are discussed. Different classification schemes are described and the problems of comparison between them are stressed. The frequency of the hypertensive disorders of pregnancy in different countries and groups at special risk are discussed. Recommendations are made on the types of research and health care needed to combat the problem.