We examined the effects of endotoxin and aqueous extracts of flax dust on isolated canine tracheal smooth muscle with and without epithelium and on human platelets. Incubation with endotoxin for 60 minutes neither contracted resting airways nor relaxed airways contracted with acetylcholine or histamine. Endotoxin also failed to promote 5-HT release from platelets as well as aggregation of these platelets. Extracts of flax dust produced airway contractions similar to those elicited by extracts of senescent cotton bracts in that they were of equal magnitude and could be blocked with atropine. Flax extracts also elicited a modest release of 5-HT from human platelets but, in contrast to cotton dust extracts, contained no measurable tannin.