OBJECTIVE To explore the effect of montelukast on bradykinin-induced tracheal smooth muscle contraction of isolated guinea pig trachea. METHODS To study the effect of bradykinin in the absence and in the presence of montelukast on the isolated tracheal smooth muscle of a guinea pig pretreated with indomethacin (10(-6)M), phentolamine (10(-5)M), and propranalol (10(-6)M), to eliminate the effect of endogenous prostaglandins and catecholamines. The trachealis smooth muscle activity was recorded through the Isometric Force Displacement Transducer on a Four Channel Oscillograph. A cumulative dose-response relationship was demonstrated by adding successive doses of bradykinin on the tracheal strips, starting with 11 μg to 77 μg of 10(-4) concentration. A similar procedure was repeated in the presence of montelukast 0.5 μg/ml, which, was equal to approximate C(max) achieved in vivo with a 10 mg oral dose of montelukast, and in the presence of 1 μg/ml of montelukast. METHODS Data was expressed as mean ± standard error (SEM), and was analyzed using the SPSS version 15. A P value of less than 0.05 was considered significant. RESULTS Bradykinin produced a dose-dependent, reversible contraction of isolated tracheal smooth muscle. Montelukast significantly reduced the bradykinin-induced tracheal smooth muscle reactivity and shifted the bradykinin curve to the right and downwards, in the presence of both concentrations of montelukast. The mean magnitude of response achieved with 77 μg of bradykinin in the absence of montelukast was 39 mm ± 6.26, in the presence of 0.5 μg/ml of montelukast it was 24.17 mm ± 4.11, and in the presence of 1 μg/ml of montelukast it was 13 mm ± 2.6. CONCLUSIONS It is concluded that montelukast significantly inhibits, in a dose-dependent manner, the bradykinin-induced contraction of the guinea pig tracheal smooth muscle, and alludes to an interaction between the bradykinin and leukotriene mediators.