Some of the leading scientists in the field of hypertension accepted an invi- tation to actively participate in an international symposium on primary hypertension. Scientists from 13 countries - from western, southern, and eastern Europe, Australia, and the United States - were present. The meeting was held in Cologne in March 1985. After previous meetings and workshops at Titisee in the Black Forest and several symposia on the renin- angiotensin-aldosterone system here in Cologne, this symposium on prima- ry hypertension was organized in order to induce and to stimulate critical discussion on the basic pathogenetic mechanisms involved and the recently established therapeutic implications. Numerous studies have been based on the concept that the elevation in blood pressure is mediated by several vasopressor substances. For this reason the renin-angiotensin system has been considered to be the essential endocrine mechanism involved in developing and sustaining arterial hyper- tension. Other vasopressor factors, such as catecholamines, vasopressin, and serotonin, have been studied extensively and were assumed to play additional parts in blood pressure regulation. However, several other ap- proaches have been initiated in recent years.