Ethephon (2-chloroethylphosphonic acid) was applied to flue-cured tobacco plants subjected to variations in cultural regime and harvesting technique to determine its influence on maturation, yield and quality. The response to ethephon treatment was evident in ripe or nearly ripe leaves after 3 days. Ethephon treatment usually caused a reduction in grade index and in content of reducing sugars, but yield and content of total alkaloids were largely unaffected by such treatment. Quality deterioration of leaves from low or middle stalk positions occurred during the curing process even though such leaves were harvested prior to the color change (yellowing) indicative of treatment effect. In spite of quality deterioration from ethephon treatment, cigarettes made from treated leaves were preferable to cigarettes made from untreated leaves. The potential of ethephon treatment would appear to be greatest for leaves at upper stalk positions, which are most likely to be damaged by frost. Such leaves responded to ethephon, if ripe or nearly so, without undergoing significant quality deterioration.