A virus was serendipitously isolated, presumably a contaminant of fetal bovine serum, and designated Seneca Valley Virus-001 (SVV-001). SVV-001 has oncolytic activity against adult tumors with neuroendocrine features but is not harmful to normal human cells. The complete genomic sequence of SVV-001 was determined and shown to have a typical picornavirus genomic structure. Twelve additional viruses have been isolated from pigs in various locations in the USA that appear to be related to SVV-001. The sequences of two genomic regions (VP1 and the 3' end) of six of the isolates were determined and analysis showed that all were closely related to SVV-001. The isolates and SVV-001 are also serologically related as antisera from one virus recognizes all isolates. Additionally, the selectivity of one of the isolates is identical to SVV-001. Phylogenetic analysis demonstrates that SVV-001 is most closely related to, but is clearly different, from members of the genus Cardiovirus; therefore, they should be classified as a new species (suggested name Seneca Valley virus) in a new genus (suggested name Senecovirus). Serological surveys revealed the presence of antibodies capable of neutralizing SVV-001 in pigs, cattle and mice, but not in humans. Attempts to infect pigs with SVV-001 and two of the related isolates failed to demonstrate any specific disease. SVV-001 has novel features which make it an attractive systemically deliverable oncolytic virus therapy.