The IDEXX Swine influenza virus H1N1 and H3N2 enzyme-linked immunosorbent assays (ELISAs) are used worldwide, but their capacity to detect antibodies to European Swine influenza viruses (SIVs) has not been documented. A total of 313 well-defined sera from SIV seronegative pigs and pigs experimentally infected with European SIVs were used to compare the performance of both ELISAs and the hemagglutination inhibition (HI) test. The ELISAs largely failed to detect pigs that had been infected with H1N1 (0/42 positive in H1N1 ELISA) or H3N2 only (9/18 positive in H3N2 ELISA; group 1). Higher ELISA detection rates were found after consecutive infection of pigs with either H1N1 or H3N2 and 1 other subtype (7/40 and 11/22 positive in H1N1 and H3N2 ELISA, respectively; group 2). Of 39 pigs that had been vaccinated twice with 1 of 4 commercial SIV vaccines (group 3), 25 tested positive in the H1N1 and 4 in the H3N2 ELISA. Pigs that had received a single vaccination after a prior infection with H1N1 and/or H3N2 (group 4) were more frequently positive than group 1 or 3 pigs (23/24 and 15/24 positive in H1N1 and H3N2 ELISA, respectively). Both the H1N1 and H3N2 ELISA showed a low sensitivity (39% and 35%, respectively) relative to the HI test. Because pigs in the field are frequently infected and/or vaccinated with multiple SIV subtypes and variants, they are more likely to test positive in the ELISAs. However, the interpretation of ELISA results will be difficult, and HI remains the method of choice.