The inhibitory capacity of calcium antagonists on basophil histamine release was examined in allergic patients and in controls. All dihydropyridines tested (nifedipine, nimodipine, nitrendipine, nicardipine, felodipine) dose-dependently inhibited anti-IgE- and A23187-induced release with an order of potency of felodipine greater than nicardipine greater than nifedipine = nimodipine = nitrendipine. Only the inhibition induced by felodipine and nicardipine on anti-IgE-induced release could be counteracted by increasing extracellular calcium. Diltiazem, not belonging to the dihydropyridines, was a weak inhibitor. A combination of felodipine and verapamil in low concentrations exerted a synergistic inhibitory effect on histamine release, whereas this was not the case with other combinations of antagonists. The results suggest differences in the mode of action of the 1.4-dihydropyridines. This might be of significance in the search for calcium antagonists suitable in the treatment of allergic diseases.