The cotton (Gossypium hirsutum L.) germplasm lines AGC85, AGC208, and AGC375 (Reg. no. GP- , PI ) were developed by the USDA-ARS and Cotton Incorporated. The lines possess superior fiber length and strength characteristics and improved yield performance under heat stress environments. The lines are being made available to public and private breeders as resources for concurrent improvement of fiber quality and heat tolerance in upland cottons of the mid-south and southeastern United States and as resources for the improvement of heat tolerance in Acala cottons of the southwestern and western United States. All three germplasm lines originate from the cross of the commercial cultivars ‘FiberMax958' and ‘SG248'. Advanced generation testing of AGC85, AGC208, and AGC375 was conducted in replicated trials at Tifton, GA, Maricopa, AZ, and Shafter, CA in 2004. Averaged over locations, the lint yields of AGC85 (2021 kg ha-1) and AGC375 (1874 kg ha-1) were equivalent to that of SG747 (1938 kg ha-1), and superior to the high fiber quality cultivars FiberMax 958 (1651 kg ha-1) and Phytogen 72 (1467 kg ha-1). Fiber lengths (UHM) of lines AGC208 and AGC375 (30.2mm and 29.5mm) were superior to that of the FiberMax 958 parent (28.7mm) when averaged across locations. Line AGC85 exhibited a fiber length equivalent to the FiberMax 958 parent. Fiber bundle strengths of AGC85 (33.3cN), AGC208 (32.9cN) and AGC375 (33.6cN) were stronger than the FiberMax 958 parent (31.4cN). Two lines, AGC85 and AGC375, exhibited fiber strength equivalent to that of Phytogen 72 (34.0cN). Seed of the lines will be available to public and private research and improvement efforts following the joint release by the USDA-ARS and Cotton Incorporated.