Biological and ecological data collected on a genetically modified crop and an appropriate control are useful for assessing potential ecological risk. Specific characteristics studied are selected on the basis of relevance to potential ecological effects, are well known, and are accepted by plant breeders. In these studies, germination, vegetative and reproductive growth, or ecological characteristics of Roundup Ready Flex cotton, MON 88913 were compared with a negative control, MON 88913(-). Statistically significant differences, when detected, were considered in the context of the genetic variation known to occur in cotton and their potential impact on plant pest (weed) potential (ecological risk). Experimental results revealed no effects of the genetic modification that would result in increased pest potential or ecological risk of MON 88913 compared with MON 88913(-).