Abstract: Effects of methylflavonolaminethy(4'-methyl-7-2-hydroxy-3-isopropy-laminopropoxy)-flavone hydrochloride,MFA)on the tension and cAMP content of isolated guinea pig tracheai smooth muscle strips were studied.MFA(0. 03～0. 6 mmol·L^-1)dose-dependently reduced KCl,acetylcholine(ACh )and histamine ( Hist)-induced contractions with intracellular increase in cvclic AMP.The reduction in contraction。and increase in cAMP were well correlated positively.MFA(0. 03 mmol·L^-1)showed synergism with isoprenaline(Iso)and aminophylline(Ami)in bronchodi- lation.The synergism with Iso but not Ami was accompanied by an increase in cAMP Ievels. It is suggested that the MFA-induced bronchodilation is related to the increase in intracellular cAMP level。The calcium antagonistic effect may be involved in MFA-induced bronchodilation.