Previous research at the University of Arkansas has shown that the plant growth regulator PGR-IV significantly enhanced cotton shoot growth and yield. Field and growth room studies were used to determine the effect of in-furrow application of PGR-IV on root and shoot development, and yield of cotton. In the field study, an in-furrow application of PGR-IV @ 1 oz/acre at planting followed by two foliar applications of 4 oz/acre at pinhead square and first flower increased yield by 18% compared to the untreated control, and by 11% compared to the 2-foliar applications of 4 oz/acre each at pinhead square and first flower. Growth room studies revealed that the in-furrow applications of PGR-IV resulted in dramatic increases in root length (+47%), root dry weight (+29%), number of lateral roots per plant (+75%), and nutrient uptake one week after planting. These differences were still apparent five weeks later at pinhead square but to a lesser degree. The yield enhancement from the in-furrow application was associated with enhanced root growth and nutrient uptake, whereas the yield enhancement from the foliar applications was associated with increases in leaf photosynthesis, nutrient partitioning, and boll number, whereas the yield enhancement from the positive effect of PGR-IV on root growth and accelerated early-season growth could have very substantial benefits in cotton production.