Roundup Ready cotton expresses the selectable marker protein neomycin phosphotransferase (NPTII), while Roundup Ready Flex cotton does not. This ImmunoStrip was developed and validated to determine the presence or absence of NPTII protein in single seeds of Roundup Ready cotton and to confirm the absence of the NPTII protein in single seeds of Roundup Ready Flex cotton. This ImmunoStrip is appropriate only when testing varieties of (Roundup Ready cotton, which expresses the NPTII protein) and varieties of (Roundup Ready Flex cotton, which does not express the NPTII protein). Testing any stacked-trait events, such as Bollgard II with Roundup Ready cotton is not recommended. Only Roundup Ready and Roundup Ready Flex events listed are appropriate for testing. Composite testing of seeds and leaves is also not recommended. The NPTII ImmunoStrip test will detect only the NPTII protein and has shown no cross-reaction with PAT/bar, PAT/pat, Bt-Cry1Ac, Bt-Cry2Ab or Bt-Cry1F.