Because the Federal Communication Commission's (FCC) decision to deregulate commercial radio has created great controversy over what constitutes "public interest" in broadcast deregulation, this paper provides a brief historical analysis of the bases for defining the public interest standard in broadcast regulation and examines the use of marketplace forces in defining the public interest in radio deregulation decisions. After the introduction of the problem, the first part of the paper traces the origin of the public interest standard and the arguments the regulators have used to rationalize their public interest determination. The paper then explains how the FCC has based it movement toward deregulation on the idea that marketplace forces, not government regulations, have come to dominate commercial radio. Major arguments against the FCC's view are then reported, and the ways in which the FCC has modified its reliance on the marketplace model are detailed. The paper concludes with a lengthy discussion of the entire controversy, pointing up weaknesses and inconsistencies in the FCC's use of the marketplace model. (JL)