Effects of sublingual administration of nifedipine on systemic arterial pres sure (BP), plasma renin activity (PRA), aldosteron level (AL), and serum so dium (Na) and potassium (K) levels, have been determined. A significant decrease was observed in systolic and diastolic blood pressure five minutes after the sublingual administration of nifedipine in 21 patients with mild or moderate essential hypertension. Furthermore, in an observation period of six hours, it was also established that the effect of nifedipine on systolic and diastolic blood pressure continued. An increase was observed in glomerular filtration rate, whereas there were no changes in PRA, AL, or serum Na and K levels.