The structural proteins of several isolates of the Indiana serotype (Orsay, Glasgow, and San Juan) of vesicular stomatitis virus (VSV) were compared by sizing peptides generated by digestion with Staphylococcus aureus V8 protease or α-chymotrypsin. These digestions yielded nearly identical peptide patterns for all the VSV proteins except for the glycoprotein, indicating that the major surface antigen, even of these closely related isolates, is subject to change. When two serologically distinct VSV isolates (Indiana and New Jersey) were similarly examined, each protein had a peptide pattern characteristic of that serotype. The glycoprotein of the two serotypes had no peptides in common, while the internal viral proteins L, N, NS, and M showed various degrees of similarity. Digests of the L (polymerase) and M (membrane) protein, in particular, generated groups of small peptides with identical mobilities, suggesting that there may be core regions in the Indiana and New Jersey strain which are conserved. These conserved regions may in turn represent essential functions of rhabdovirus proteins and are promising targets for broad-spectrum antivirals. © 1979.