Since 1993, the Centers for Disease Control and Prevention (CDC) has recommended routine HIV counseling, testing, and referral (HIV CTR) in US hospitals with an HIV prevalence >1%. Over the past 11 years, these guidelines have been revised and reiterated but they have not successfully been incorporated into standards of care;an estimated 310,000 persons are living in the US with undiagnosed HIV infection. One obstacle to broader adherence to national standards is that the guidelines fail to address the practical question of who should do the testing: Can busy providers add HIV CTR to their practice or must additional support services be provided? Keying off the Systems Model of Clinical Preventive Care and its emphasis on both provider and patient factors in determining the success of preventive behaviors, we propose to study alternative approaches to the delivery of HIV CTR in an urban hospital emergency department (ED) setting. Our two specific aims are: 1) To conduct a randomized, controlled trial of rapid HIV testing comparing ED provider-based testing with HIV counselor-based testing. We will identify: a) The strategy that maximizes the acceptability of HIV testing to patients b) The strategy that maximizes linkage to care among detected, HIV-infected patients 2) To evaluate the cost-effectiveness of the alternative HIV CTR strategies We will examine the intersection of provider and counselor predisposing, enabling and reinforcing factors with trial outcomes of HIV test offer, acceptance, and linkage to care rates. Clinical and economic evaluation will inform policies to promote routine HIV CTR as standard practice. Led by Rochelle P. Walensky, MD, MPH, the project team has an extensive track record of successful routine HIV CTR program design, effective HIV diagnosis and linkage to care, and HIV CTR economic evaluation. The scientific basis for early detection of HIV infection and aggressive linkage to care has been successfully laid. The challenge now is to identify effective, affordable, and cost-effective implementation mechanisms.