Pandemic H1N1 influenza virus (pan-H1N1) was first reported in Mexico in April 2009, followed by rapid spread in different countries (1). Although the origin of the 2009 pan-H1N1 is unclear, the virus is genetically closely related to the triple reassortant (TR) swine influenza viruses (SIVs) currently circulating in pigs. Classic SIV H1N1 has been widely reported since an influenza-like outbreak was first detected in pigs in the United States (US) during the catastrophic human influenza pandemic of 1918 (2). . Classic H1N1 SIVs were exclusively prevalent among swine populations in the United States before the appearance of new TR H3N2 viruses in 1998. The genes for TR H3N2 viruses originated from viruses of human, swine, and avian lineage. This specific constellation of internal genes is called the TR internal gene (TRIG) (3). Currently, classical, TR, and human-type H1 viruses are circulating in the U.S. swine population (4). Pigs are susceptible to influenza viruses of different origins and are considered mixing vessels for genetic reassortment (3), thus 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 highlight reassortment events between swine viruses and pandH1N1 (6, 7). Here we report the isolation of novel reassortant H1N2 influenza viruses with genes derived from contemporary pig and 2009 pandH1N1 viruses. In October and November 2010, saliva samples were collected from 5-month-old and 8-month-old piglets, respectively. weeks, showing mild respiratory signs of cough and depression. The farms are 30 miles apart with different military personnel. Filtered samples were inoculated into the dog Madin Darby k...... middle 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, warranting further investigation into 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, the new isolates are the first porcine and pandH1N1 reassortant identified in the United States. The reassortment of pan-H1N1 with swine influenza viruses indicates the importance of systematic surveillance of the swine population to determine the origin, prevalence of similar reassortants in the United States, and their impact. on pig production and public health.