Mounting interest in host immunity and understanding the pathogenesis of disease has focused attention on the identification of T lymphocyte epitopes within various antigens. This effort has proven troublesome because of time and financial constraints. We have developed a cost-effective technique that allows for the rapid identification of these antigenic sequences within proteins of interest. Using a panel of in vitro synthesized peptides and a CD4+ bovine T lymphocyte cell line, we have identified a single epitope on a herpesviral envelope glycoprotein. In the future, this technology should allow epitope mapping to be more practical for a large number of antigens.