We have studied the possible interactions between nifedipine and digoxin in 8 healthy subjects in two ways: A. The effect of digoxin (0.25 mg, tablet q.d. for 8 days) on the pharmacokinetics of nifedipine following single-dose (10 mg capsule) administration. Mean values for peak concentration, area under the serum concentration time curve (AUC), total serum clearance and the half-life of elimination of nifedipine did not differ before and concomitantly with digoxin administration. B. The effect of nifedipine (30 mg t.i.d.p.o. for 6 days) on the pharmacokinetics of digoxin following single dose (0.5 mg i.v.) administration. No significant differences were found between the mean values of the half-life of the alpha and beta phases, the AUC and the apparent volume of distribution of digoxin before and concomitantly with nifedipine administration. However, during the later period, the mean cumulative 96 h urinary excretion of digoxin increased by 18% (p less than 0.05) and the renal clearance of digoxin by 26% (p less than 0.05). No change was found, however, in the total plasma clearance of digoxin.