A model of experimental allergic asthma was induced by sensitizing and challenging guinea pigs with egg albumin. The changes on the concentrations and affinities of ?2,? adrenergic and muscarinic receptors as well as the content of cyclic adenosine monophosphate in lung tissue of the asthmatic animals were investigated and compared with the values obtained from normal animals respectively. The results showed that the maximal binding volume of ? receptor as well as the content of cAMP decreased significantly, while the concentrations of ?2, receptor and M receptor increased. It is well known that the ? receptor mediates a process resulting in the relaxation of bronchial smooth muscle by stimulating adenylate cyclase and therefore, increases the cytoplasmic concentration of cAMP. whereas the ?2, and M receptor mediate processes resulting in the contraction of smooth muscle through quite different mechanisms. The significance of the two kinds of change operating towards opposite direction in the pathogenesis of allergic asthma was discussed.