An excellent source of additional genetic diversity for Upland cotton, Gossypium hirsutum, is the secondary gene pool of Pima cotton, G. barbadense. Unfortunately, this interspecific cross quickly segregates back to parental types which, in turn, makes using this germplasm resource very inefficient. To more effectively utilize this resource, a series of near-isogenic introgression lines (NIILs) are being developed from a Tamcot 2111 by Pima S-6 interspecific backcross program. RFLP markers are utilized to monitor the segregation of Pima S-6 donor DNA in backcrosses to Tamcot 2111. This provides a series of lines that each contain single small chromosome segments with the intent to cover the entire Pima S-6 genome. Fiber quality traits were measured in the first subset of this series to monitor phenotypic effects of these DNA segments.