In an earlier study we reported that detached cotton flowers produced sufficient ethylene before the period of natural abscission to suggest that ethylene might be a natural regulator of young fruit abscission. The present report explores this probability further. Intact cotton (Gossypium hirsutum L.) fruits produced ethylene at rates as high as 36 mul ethylene/kg fresh wt.hr during the 2 days before they abscised. Direct measurements of ethylene in gas samples withdrawn from fruits indicated that production of 1 mul ethylene/kg fresh wt.hr is equivalent to an internal concentration of approximately 0.1 mul/l. Fumigation of fruiting cotton plants with only 0.5 mul/l caused 100% abscission of young fruits and floral buds within 2 days. This correlated with the estimated endogenous levels of ethylene. Reduced pressure, which reduced the internal levels of ethylene, delayed abscission of young fruits and leaves, a result which supports our conclusion from this study- that ethylene is one of the regulators of young fruit abscission in cotton.