The pestivirus genome encodes a single polyprotein which is subject to co- and posttranslational processing by cellular and viral proteases. The map positions of all virus-encoded proteins are known with the exception of a hypothetical peptide (p?) which interlinks the glycoprotein E2 and the nonstructural protein NS2-3 approximately between amino acid positions 1060 and 1130. Expression studies with recombinant vaccinia viruses bearing a set of C-terminally truncated E2-p?-NS2-encoding sequences derived from a bovine viral diarrhea virus (BVDV) strain led to the identification of a minor fraction of E2 which had an increased molecular mass due to a C-terminal extension. This larger form of E2 (E2p7) was specifically recognized by an antiserum raised against the amino acid sequence from 1065 to 1125. In addition, the antibodies revealed a BVDV-encoded 7-kDa protein (p7) in infected cells. By radiosequencing it was determined that Val-1067 was the N-terminal amino acid of in vitro-synthesized p7. Analyses of BVDV and classical swine fever virus virions suggest that neither p7 nor E2p7 is a major structural constituent.