Maintaining varietal and transgenic purity in foundation seed stocks has become more challenging in recent years. The purpose of this study was to evaluate pollen dissemination between two adjacent fields of genetically-enhanced cotton in the Mississippi Delta in 2000 using seed bioassays. Fields located south of Leland, Mississippi were planted with experimental Stoneville varieties containing BXN®/Bollgard® and Roundup Ready®/Bollgard traits. These fields were separated by a 13-foot road. At harvest maturity, 50-boll samples were collected randomly by hand from the bottom, middle, and tops of plants. A BXN® bioassay was used to quantify dissemination of pollen from the BXN field into the RR field by measuring resistance of seedlings to bromoxynil [(3,5-dibromo 4-hydroxybenzonitrile) (BUCTRIL® 4EC)] herbicide. A Roundup Ready® rolled towel bioassay was used to quantify dissemination of pollen from the RR field into the BXN field by measuring resistance of seedlings to glyphosate (ROUNDUP ULTRA®) herbicide. Pollen dissemination from the BXN field to the RR field averaged 1.89% in Row 1 nearest to the road, followed by 0.77% in Row 8, 0.13% in Row 16, and 0.00% in Row 24. Pollen dissemination from the RR field to the BXN field averaged 1.05% in Row 1 nearest to the road, and 0.69% in Row 8. Leaving 8 border rows un- harvested in seed production fields appears reasonable in this production environment to avoid potential contamination from adjacent fields of different varieties, unless a zero tolerance for unintended transgenic events exists.