The world is experiencing a pandemic of swine-origin influenza virus H1N1. A vaccine to prevent disease is now available, and millions have or will become ill before they can be vaccinated. The ability to use swine-origin influenza virus vaccines as a public health tool has been described as a "race against time." Oseltamivir and related drugs are being used in an effort to reduce morbidity and mortality, but their efficacy for treating severe influenza is suboptimal, and possible wide-spread emergence of oseltamivir-resistant mutants is a concern. Another approach for prevention and treatment of serious influenza is infusion of hyperimmune plasma. The United States has thousands of licensed blood product collection centers that produce millions of liters of plasma licensed by the Food and Drug Administration on an annual basis for the treatment of serious conditions. Immunotherapy using infusion of convalescent plasma (or hyperimmune intravenous immunoglobulin) has been reported to be an effective treatment for severe influenza and other virulent pathogens in animal models and humans. Plasma obtained from those that have recovered or were early recipients of vaccine offers a resource for production of an immediately available and potentially effective therapy at the local, state, and national level. Past, current, and future uses of immunotherapy and current advisory body recommendations for this approach are presented.