There are two major mechanisms by which a contraction can be mediated in airway smooth muscle, namely either a receptor-operated contraction or a depolarisation-induced contraction. Glucan from baker's yeast, an insoluble, particulate glucan, can induce hypo-responsiveness to methacholine-induced (a receptor-operated contractile agent) contractions in guinea pig respiratory smooth muscle. The present experiment was designed to determine whether this effect was either specific to methacholine, or part of a more general hypo-responsive phenomenom. Using immersed trachea and pefused lung tissue models, contractions were produced with one of a number of constrictor agents. The effect of exposure of the airway smooth muscle to 50µg/ml glucan (from baker's yeast) on these responses was then determined. This glucan caused some degree of hypo-responsiveness to all contractile agents used. This suggests that baker's yeast glucan acts by a non-specific mechanism.