On occasion, blood pressure rises so precipitously and severily, or the clinical setting in which hypertension occurs is so critical, that prompt pressure lowering becomes crucial to prevent disabling, or even lethal complications. Such hypertensive emergencies more commonly complicate the accelerated phase of untreated or poorly treated hypertension of various etiologies. There is also a group of conditions that qualify as hypertensive emergencies not so much because of the actual height of the pressure, but rather because of complicating disorders that make even moderate pressure elevation harmful. These include aortic dissection, intracranial bleeding and acute left ventricular failure. Two fundamental concepts in the management of hypertensive emergencies are: immediate and effective therapy is required and takes precedence over time-consuming diagnostic procedures; the choice of the drugs will depend on how their time course of action and hemodynamic and metabolic effects meet the needs of the clinical situation. It is well proven that nifedipine reduces Ca-dependent vascular smooth muscle tone by direct interference with transmembrane Ca supply and thereby counteracts every kind of contractile tension development of the vascular wall: the higher the wall tension, the easier relaxation in induced by a given concentration of the compound. Because of this, it has become quite clear from recent studies that: nifedipine is a potent antihypertensive agent.(ABSTRACT TRUNCATED AT 250 WORDS)