The main objective of this study was to determine the effect of intracrystalline and intercrystalline swelling agents and reactive dyes on the accessibility of cotton cellulose to commercial cellulase enzymes. Both types of swelling agents improved the accessibility, and intracrystalline swelling agents showed better results, as the accessibility to difficult-to-reach crystalline regions was increased. As expected, the reactive dyes inhibited the accessibility of the enzymes to some extent. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121:1946-1950, 2011