1. Anaphylaxis was induced in the isolated heart of the guinea-pig in the presence of burimamide at concentrations of 4 x 10(-5)M and 2.7 x 10(-4)M.2. Burimamide did not affect the immunological release of histamine; however, it selectively antagonized the positive inotropic and chronotropic effects of released histamine. The antagonism of the positive chronotropic effect was concentration-dependent.3. Neither the negative dromotropic effect nor the decrease in coronary flow rate occurring during anaphylaxis were inhibited by burimamide.4. The results are in agreement with the double histamine receptor theory and suggest that, in the heart of the guinea-pig, H(2)-receptors are involved in the positive inotropic and chronotropic effects of released histamine, and H(1)-receptors in the negative dromotropic effect.