Field experiments were conducted in 1991 and 1992 near Stoneville, MS and Greenville, MS, to determine the impact of pyrithiobac on cotton fruiting, maturity, and yield. Trials were conducted in areas maintained weed-free with standard production practices to optimize yields. Pyrithiobac was applied at 105 or 210 g ae/ha either PRE or POST to cotton in the cotyledon to 2-leaf, 5- to 7-leaf, and matchhead-square (MHS) stages of growth. At one location, monosodium salt of methylarsonic acid (MSMA) and fluometuron plus MSMA were applied as standard comparisons. At the Stoneville location, injury 1 wk after treatment (WAT) with pyrithiobac ranged from 2.5% with 105 g/ha applied at cotyledon to 2-leaf to 26% with 210 g/ha applied at MHS. Injury was transient in nature and was rarely detectable 4 wk after treatment in either year. Injury was not evaluated at the Greenville location. At Stoneville, a reduction in height occurred with MHS applications of pyrithiobac and MSMA. There was no reduction in yield for any treatment compared to the untreated check in 1991 at Stoneville and in both years at Greenville. In 1992 at Stoneville, treatments of 210 g/ha pyrithiobac, MSMA, and fluometuron plus MSMA at all application timings reduced yield. Pyrithiobac at 105 g/ha applied PRE also reduced yield. Greatest yield loss occurred with treatments of MSMA applied at MHS. There were no yield reductions at either location with postemergence application of 105 g/ha pyrithiobac.