Three studies have been conducted at Stoneville, MS, from 1982 through 1989 to evaluate the response of cotton to late-season or delayed sidedress nitrogen applications of urea-ammonium nitrate solution (32% N). Two soil types, Dundee very fine sandy loam and Dundee silt loam (Aeric ochraquepts), were used to provide input from different soil types. In different treatments, the sidedress nitrogen was applied between early square and peak bloom and accounted for one-half of the total nitrogen. In the first study (1982-1985) the total nitrogen rate was 80 lb N/A. In 1986, the N rate was increased to 100 lb N/A with two soil types. Total seed cotton yield was measured each year from two harvests at each location. Comparisons were made between the most common application system (100% preplant) and the various timings of sidedress application. In the initial study (Dundee very fine sandy loam, 1982-1985), the response to delayed sidedress ranged from 5.5 to 10.1% with an average gain of 7.5%. When the N rate was increased to 100 lb N/A, the yield response was similar, ranging from 2.7 to 11.2% with an average of 7.7% (237 lb/A). The yield response was also positive on the Dundee silt loam but the magnitude was smaller with only a 4.1% increase compared to the 100% Preplant system and 8.4% compared to sidedress applications at the pin head square growth stage. The greatest yield increase percentage has been observed at the second harvest without decreasing maturity. In the first study, the second harvest yield increase was 31%. The percent first harvest (PFH) was decreased when the nitrogen was applied at mid-bloom but did not delay maturity as the yields at the first harvest were equal to or higher with delayed sidedress as compared to preplant. The decrease that was observed resulted from an increase in seed cotton at the second harvest relative to the first harvest. If there had been a true delay in maturity, the first harvest yields would have been lower. The late-season soil nitrogen was effective in the development of the top bolls which produced the increase in second harvest.