EPA is issuing significant new use rules (SNURs) under section 5(a)(2) of the Toxic Substances Control Act (TSCA) for two chemical substances which were the subject of Premanufacture Notices (PMNs). The two chemical substances are identified generically as multi-walled carbon nanotubes (MWCNT) (PMN P-08-177) and single-walled carbon nanotubes (SWCNT) (PMN P-08-328). This action requires persons who intend to manufacture, import, or process either of these two chemical substances for a use that is designated as a significant new use by this final rule to notify EPA at least 90 days before commencing that activity. EPA believes that this action is necessary because these chemical substances may be hazardous to human health and the environment. The required notification would provide EPA with the opportunity to evaluate the intended use and, if necessary, to prohibit or limit that activity before it occurs.