The effects of fiber reactive and direct dyes on certain physical properties (tenacity, elongation, and initial modulus) of cotton fibers were investigated. Raw cotton fiber and raw yarn spun from the same batch of fiber were obtained. Fiber and yarn were processed by scouring, bleaching, and dyeing with both dyes, using an Ahiba Texomat Dyeing Apparatus, and the appropriate chemical systems. Fibers from treated fiber and fibers removed from treated yarns were tested after each treatment step, using an Instron Tensile Tester. The Wilks multivariate F test was used to determine whether or not significant differences existed between sequential treatments, and between fibers treated as fiber or as yarn. When significant differences were indicated, univariate analysis of variance was computed to identify the property(s) responsible. The results of this study indicated that the physical properties of both fiber reactive dyed and direct dyed fibers were not significantly different from each other or from the bleached fiber from which they were dyed. The properties of bleached (and dyed) fibers were significantly different (lower tenacity and elongation, higher initial modulus) from untreated or scoured fibers, indicating that the bleaching step was responsible for most of the changes noted. The properties of fibers treated as fiber were generally different (lower tenacity, higher elongation, lower initial modulus) than those of fibers removed from yarn. / M.S.