The precise role of neurogenic and humoral mechanisms in the pathogenesis of hypertension cannot be defined. Most likely several mechanisms are interacting. These may differ in the early phases of hypertension if trigger mechanisms are involved and in later phases of sustained hypertension if adaptive changes create a situation of hyperresponsiveness even to normal stimuli. The mechanisms discussed in this review may apply to normal circulatory regulation as well as to human essential, renal, steroid, neurogenic, or different experimental models of hypertension. No attempt is made to assign specific mechanisms to certain types of hypertension. In some types, more than one proposed mechanism may be active.