In vivo and in vitro experiments have strongly indicated that mast cell degranulation, with its release of histamine and other pharmacoactive compounds, plays a major role in the acute respiratory response of humans following inhalation of cotton textile dust. Heliocides H(1), B(1), B(2), and gossypol stimulate significant mast cell degranulation at concentrations well below those found in mill dust from glanded cotton. Daily mast cell degranulation, stimulated by these terpenoids aldehydes, could account for many of the pathophysiological changes which have been found in the chronic byssinotic.