Four years of research were conducted (1982-1985) at Stoneville, MS, on a Dundee very fine sandy loam (Aeric Ochraqualfs) to evaluate the response of cotton to late-season sidedress applications of urea-ammonium nitrate solution (32%). In different treatments the sidedress nitrogen was applied between early square and peak bloom and accounted for one-half of the 80 lb N/A applied. Foliar N was also applied as a treatment which compared late foliar N to the soil-applied sidedress system. Total seed cotton yield was measured from two harvests each year. Comparisons were made between the most common application system (100% preplant) and the others. The yield increase with the late sidedress application ranged from 5.5 to 10.1% and averaged 7.5% over four years compared to the all-preplant system. The foliar applications reduced yields from 0.03 to 4.4% with an average reduction of 2.6%. The greatest yield increases with the late-sidedress system have occurred in the second harvest with a 4-year average yield increase of 31%. For the first harvest, the seed cotton yield increase averaged 4.0% over the four year period as compared to the 100% preplant treatment. The percent first harvest (PFH) was decreased when the nitrogen was applied as a late sidedress but did not delay maturity. The decrease that was evident, resulted from the increase in seed cotton that was harvested at the second picking in relationship to the total. If there had been a true delay in maturity, the first harvest yield would have been lower rather than higher. The late-season soil nitrogen was effective in the development of late season bolls which were responsible for the subsequent increase in yield. The same yield response was not evident when the nitrogen was applied to the foliage.