A system dynamics modeling method was developed to predict changes in plasma renin activity (PRA), plasma aldosterone (PA) and electrolyte concentrations in response to diuretic stimulation in patients with primary aldosteronism. Its clinical validity was evaluated by comparing experimental and simulation results. In a clinical experiment, furosemide 20 mg was given by intravenous injection to 20 patients with primary aldosteronism. PRA, PA and electrolyte concentrations were measured hourly for 3 hours after administration of the drug. The computer simulation outputs were consistent with the experimentally measured values at each corresponding point of time. An analysis of model predictions indicates that the method may predict the changes in PRA, PA and electrolyte concentrations after diuretic administration in accordance with a time interval.