At the end of 2003, an estimated 1 million persons in the United States were living with human immunodeficiency virus (HIV) infection, including those with acquired immunodeficiency syndrome (AIDS); approximately one fourth of these persons had not had their infections diagnosed. In 2003, CDC implemented a new initiative, Advancing HIV Prevention (AHP), focused, in part, on reducing the prevalence of undiagnosed HIV infection by expanding HIV testing and taking advantage of rapid HIV tests that enable persons to receive results within 30 minutes, instead of the 2 weeks typically associated with conventional tests. In support of AHP strategies, during September 2003-December 2005, CDC purchased and distributed rapid HIV tests to expand testing and assess the feasibility of using rapid tests in new environments (e.g., outreach settings or emergency departments). This report summarizes the results of this rapid HIV-test distribution program (RTDP), in which CDC distributed tests to 230 organizations in the United States and identified 4,650 (1.2%) HIV infections among 372,960 rapid tests administered. The results suggest that RTDP helped scale up rapid HIV-testing programs in the United States and enabled diagnosis of HIV in persons who might not have had their infections diagnosed otherwise.