Studies of etiopathogenic mechanisms of bronchoconstriction in byssinosis indicate the possible involvement of histamine, 5-HT, platelet-activating factor, and metabolites of arachidonic acid as mediators of bronchoconstriction. These substances might be released by a variety of lung and/or recruited cells to induce construction of respiratory airways characteristic of the acute byssinotic reaction. It certainly seems possible that cotton dust induces acute bronchoconstriction by more than one mechanism and that a number of factors, both endogenous and exogenous, influence the increased bronchomotor response to cotton dust inhalation in any given textile worker.