We have previously shown that replication of foot-and-mouth disease virus (FMDV) is highly sensitive to alpha/beta interferon (IFN-␣/␤). In the present study, we constructed recombinant, replication-defective human adenovirus type 5 vectors containing either porcine IFN-␣ or IFN-␤ (Ad5-pIFN␣ or Ad5-pIFN␤). We demonstrated that cells infected with these viruses express high levels of biologically active IFN. Swine inoculated with 10 9 PFU of a control Ad5 virus lacking the IFN gene and challenged 24 h later with FMDV developed typical signs of foot-and-mouth disease (FMD), including fever, vesicular lesions, and viremia. In contrast, swine inoculated with 10 9 PFU of Ad5-pIFN␣ were completely protected when challenged 24 h later with FMDV. These animals showed no clinical signs of FMD and no viremia and did not develop antibodies against viral nonstructural proteins, suggesting that complete protection from infection was achieved.