Pandemic H1N1 (pan-H1N1) influenza virus was first reported in Mexico in April 2009, followed by rapid diffusion in several countries (1). Although the origin of the 2009 pan-H1N1 virus is unclear, the virus is genetically closely related to the triple reassortant (TR) swine influenza viruses (SIVs) currently circulating in pigs. Classic H1N1 SIV has been widely reported since an influenza-like epidemic was first detected in swine in the United States (US) during the catastrophic human influenza pandemic of 1918 ( 2 ). The classic H1N1 SIVs were prevalent exclusively among swine populations in the United States before the new TR H3N2 viruses emerged in 1998. The genes of the TR H3N2 viruses were derived from viruses of human, swine, and avian lineages. This specific constellation of internal genes is called the TR internal gene (TRIG) (3). Classical, TR, and human-like H1 viruses currently circulate in the U.S. swine population (4). Pigs are sensitive to influenza viruses of different origins and are considered mixing vessels for genetic reassortment(3), therefore the co-circulation of different influenza strains, including pan-H1N1 viruses, in pigs increases the potential for the emergence of new reassortments (4, 5) , and recent reports further highlight reassortment events between swine and pandH1N1 viruses (6, 7). Here we report the isolation of novel reassortant H1N2 influenza viruses with genes derived from contemporary pigs and the 2009 pandH1N1 viruses. During October and November 2010, oral fluid samples were collected from 5- and 8-month-old weaner pigs, respectively. weeks, showing mild respiratory signs of cough and depression. The farms are 30 miles away with several military personnel. The filtered samples were inoculated into the Madin Darby canine k...... center of paper ......f of both origins. Compared to pan-H1N1 and all other reported porcine/pandH1N1 reassortants, the two US reassortant isolates demonstrated one (E16G) and four (G34A, D53E, I109T, and V313I) unique amino acid changes in the M2 and NP proteins, respectively, which deserves further investigation regarding the role of these amino acids in relation to host adaptation. The remaining four internal genes, PB2, PB1, PA, and NS, were similar to the composition of contemporary porcine TRIG (data not shown). knowledge that the new isolates are the first swine and pandH1N1 reassortants identified in the United States. Reassortment of pan-H1N1 with swine influenza virus indicates the importance of systematic surveillance of the swine population to determine the origin, prevalence of similar reassortants in United States and their impact on both swine production and public health.