The 'Spanish' influenza pandemic of 1918-1919 was the worst influenza pandemic in history, killing 40 million people worldwide in about one year. The agent responsible was not isolated in 1918. Pandemic influenza viruses have emerged twice since 1918, in 1957 and 1968. Future influenza pandemics will undoubtedly arise. An understanding of the genetic make-up of the most virulent influenza strain in history will facilitate prevention of such future pandemics. Using archival autopsy material from the 1918 pandemic, small fragments of influenza virus RNA can be isolated and sequenced. Assembling overlapping fragments, the complete genomic sequence of each gene of the 1918 strain can be deduced. In preliminary work, the hemagglutinin, neuraminidase, matrix, and non-structural gene segments have been sequenced. This application proposes to extend these findings by sequencing the remaining four gene segments: nucleoprotein and the three polymerase genes, PA, PB1, and PB2. Complete characterization of the viral genome is likely to yield insights into the origin and lethality of the 1918 virus, and is essential for an understanding of the molecular basis of the emergence of pandemic influenza viruses. Hypotheses on the virulence of the 1918 virus can only be tested once the complete genomic sequence of the virus is known. The second goal of the proposal is to place the 1918 virus in context by performing an initial characterization of the viruses that preceded and followed it. By identifying pre-1918 influenza viruses it can be determined which gene segments were replaced in the pandemic strain. The 1918 pandemic occurred in waves, with the first wave being significantly less virulent than the second. Identification of a spring wave ease would allow direct genetic comparison of the two strains and any differences would help elucidate the genetic basis of virulence of the fall wave strain. Further, by identifying influenza RNA positive cases from the post-pandemic period, 1920-1940, a comparison of the drift rate of early HINI viruses with modern ones can be made and it can be ascertained whether the unusual features of the extant 1930's influenza viruses were artifacts of culture or primary features of these viruses.