The authors investigated the effect of one-week administration of verapamil in daily therapeutic doses of 4 X 40 mg by the oral route and the effect of nifedipine in daily therapeutic doses of 3 X 20 mg by the oral route. Verapamil and nifedipine did not affect significantly the levels of thyrotropin, triiodothyronine and thyroxine nor their response after stimulation with TRH. The theoretical and practical impact of this finding is discussed in particular with regard to possible side-effects of calcium antagonists during their therapeutic use in clinical cardiology.