The effects of nifedipine and propranolol, alone and in combination, on collagen-induced platelet aggregation were studied in healthy volunteers using whole blood impedance aggregometry.No significant inhibition of platelet aggregation was found after the in vitro addition of propranolol, nifedipine or nifedipine vehicle or after nifedipine ex vivo. No interaction was found between in vitro propranolol and nifedipine, either in vitro or ex vivo.