This interim rule revises the Community Development Block Grant (CDBG) program regulations by replacing the obsolete term "central city" with a new term "principal city" in the definition of "metropolitan city" and other CDBG regulations referencing "central city." The revisions are necessary because of the recent changes to the Office of Management and Budget's (OMB) Standards for Defining Metropolitan and Micropolitan Statistical Areas (MSAs) and the announcement in 2003 of new definitions for those areas using Census 2000 data. The rule updates the affected CDBG program regulations so that the terminology used by HUD is consistent with OMB standards and the purposes of the Housing and Community Development Act of 1974.