Of the estimated 1.2 million people infected with human immunodeficiency virus (HIV) in the United States, 20% are unaware of their diagnosis. Improved methods of HIV testing could decrease this number, as well as identify those who have recently acquired HIV infection and are at the most critical stage of infectivity. People with acute HIV infection have demonstrated enhanced transmission of HIV in multiple epidemiologic and pathogenetic studies. More than 50 000 HIV infections occur annually in the United States, and 30%–50% have been attributed to persons with recent infection. The original HIV diagnostic testing algorithm was developed by the Centers for Disease Control and Prevention in 1989. Recently proposed alterations to the algorithm would incorporate advancements made in HIV diagnostic testing, thereby increasing sensitivity while reducing turnaround time and cost. Improved diagnosis of acute HIV, and HIV type 2 in particular, would be expected. Knowledge of the available laboratory methods for HIV diagnosis is essential in the fight against the spread of HIV.