The nucleotide sequence of the S peplomer gene of bovine coronavirus (BCV) has been determined. A single open reading frame of 4089 nucleotides encodes a polypeptide of 150K with 20 potential sites for addition of N-linked oligosaccharides. Expression of the cloned BCV S gene by a recombinant of Autographa californica nuclear polyhedrosis virus resulted in production of a 180K glycosylated polypeptide which was transported to the surface of the cell. Comparison of the BCV S gene with the analogous genes of murine hepatitis viruses shows that the BCV S polypeptide contains a unique domain of 138 amino acids not present in murine hepatitis virus strain JHM, but which has a partially homologous counterpart in strain A59. This domain accounts for most of the differences in size of the S gene products of these coronaviruses.