Studies were aimed at identifying, characterizing and defining the roles of the gene products of poraine transmissable gastroenteritis virus (TGEV) in pathogenesis and immunity by means of recombinant deoxyribonucleic acid (DNA) technology. Two of the viral strucutral proteins were glycosylated and one of them, the peplomer, contained regions to which antiboides could attach, thereby preventing viral growth. In order to express the peplomer protein and identify regions involved in immunity, the isolation, sequencing and expression of TGEV genes in recombinant viruses and in yeast was carried out. Seven TGEV genes were identified and sequenced. Three of the gene products, nucleoprotein, integral membrane protein and peplomer, were involved in the structure of the virus particle and have been expressed in bacteria, yeast and vaccinia virus. Specific antibodies were raised against the structural proteins and these led to the identification of a specific antibody binding site on the nucleoprotein and several specific sites on the peplomer. The peplomer protein expressed by vaccinia virus still reacted with all the specific antibodies and the relative positions of 4 antigenic sites were identified on the peplomer protein. Antisera to the peplomer expressed by vaccinia appeared to prevent viral growth and disease in piglets.