EPA is promulgating a significant new use rule (SNUR) under section 5(a) of the Toxic Substances Control Act (TSCA) which requires persons to notify EPA at least 90 days before commencing the manufacture, import, or processing of certain benzidine-based chemical substances for any significant new use as described in this rule. EPA believes that this action is necessary because benzidine-based chemical substances may be hazardous to human health and that the uses governed by this rule may result in significant exposure to workers handling those substances. The required notice provides EPA with the opportunity to evaluate any intended new uses and associated activities before the benzidine-based chemical substances can be introduced into the marketplace for a significant new use, and an opportunity to protect against potentially adverse exposure before it occurs.