Abstract: The measurement of pulmonary mechanics is a quite good method for the study of antiasthrngtics in animal experiments in vivo. In this paper, the measurement of pulmonary mechanics included pulmonary resistance (R_L) and pulmonary dynamic compliance (Cdyn). The former is an index which reflects large airway caliber and the latter is an index which reflects small airway caliber. α-Terpineol is one of the antiasthmatic principles of essential oil of Artemisia argyi. R_L was decreased and Cdyn was increased after inhalation of a-Terpineol aerosol, i e, α-Terpineol aerosol could dilate both large and small airways of normal guinea pigs. When guinea pigs which had been exposed to histamine aerosol were challeged with specific antigen, R_L was increased and Cdyn was decreased. The same result was obtained in guinea pigs sensitized actively by ovalbumin or passively by antiserum containing IgE. After inhalation of \% a-Terprneol aerosol for 2 min the changes of R_L and Cdyn by the challenge were almost totally abolished. These findings showed clearly that α-Terpineol is an effective antiasthmatic in experimental asthma in guinea pigs. Effects of α-Terpineol on pulmonary mechanics in guinea pigs were not affected by propranolol (5mg/kg, i v) and reserpine (5 mg/kg, i p). These findings showed that the bronchodilative effect of a-Terpineol was not via β-adrenocepter and did not depend on the function of adrenergic nerve.