In late 2003 and early 2004, new outbreaks of influenza A (H5N1) in poultry occurred in 8 Asian countries: China, Cambodia, South Korea, Thailand, Vietnam, Japan, Indonesia, and Laos. Over 100 cases of this infection have been reported in patients in Thailand, Cambodia, and Vietnam. The alarming fact of the disease in humans is that the overall mortality rate is approximately 50%, far higher than the 2% mortality rate of Spanish flu (8), and that, like Spanish flu, most of the deaths have occurred in young, previously healthy adults or children. Autopsies also show a similar hemorrhagic, necrotizing pneumonia, and genetic and structural studies show that the hemagglutinin of influenza A (H5N1) has some of the characteristics of the Spanish flu strain (9). Of note, only 2 amino acid changes in the receptor-binding pocket of H5 lead to a virus that efficiently recognizes receptors on human cells (10). Attempts to control this virus include widescale culling—over 100 million birds have now either died of H5N1 infection or have been killed in the attempt to control the epidemic—and immunization of poultry in some countries. Despite these attempts, many authorities now feel H5N1 is enzootic in much of the bird population of Asia, in areas that account for about one third of the global human population.