A study was conducted at the University of Arkansas Northeast Research and Extension Center at Keiser, AR, in 1989 and 1990 to determine the effect of the timing of a PREP application on yield, harvest date and lint quality. PREP was effective at opening bolls for harvest, even when applied with fewer than 10 percent of the bolls open. Total seedcotton yield was not significantly different among treatments (three application dates and an untreated check) in either year, but the time at which the seedcotton could be harvested was quite different among treatments. Lint quality data were not available for the 1990 harvest. Of all of the quality parameters investigated in 1989, only micronaire showed much response to PREP. Higher micronaire was observed for each later application date.