BACKGROUND: Quinidine appeared to increase serum digoxin levels when given with quinidine. Therefore elevated serum digoxin concentrations and clinical toxicity have been reported in patient receiving quinidine. Currently, Bayesian method which estimates the most probable parameters of the drug for each patient from population parameters data is useful approach for adjusting digoxin dosage. To increase the accuracy of Bayesian method, it is desirable to use population parameters of Korean. Therefore we evaluated the effect of quinidine on digoxin clearance in Korea. METHOD: Patient's records from 19 adult cardiac disease without CHF having normal renal and liver function from Seoul National University of Hospital respectively wre evaluated. Digoxin pharmacokinetic parameters, CL and Vd, were obtained from serum concentration of digoxin of single and combined therapy at each steady-state by using bayesian method. RESULTS: This study show that quinidine reduced the total body clearance of digoxin from 2.39+/-0.17 to 1.51+/-0.08ml/min/kg(p<0.05) and reduced the digoxin volume of distribution from 8.57+/-0.29 to 4.98+/-0.19L/kg(p<0.05). This results show that digoxin dosage reduced to 40-50% in Korean, if quinidine therapy is initiated.