The virus specificity of antibodies against bovine herpes virus type 1 was determined with a radioimmunoprecipitation assay and serum collected from natural and experimentally induced infections. By using sequentially collected sera, the development of antibodies to 4 to 5 viral glycoproteins and 11 to 12 nonglycosylated proteins was followed for the first 50 days after infection. The major and most consistent responses in experimentally and naturally infected animals were to four glycoproteins with molecular weights of 102,000, 96,000, 69,000, and 55,000, as well as to a major virion 115,000-molecular-weight nonglycosylated protein. The four glycoproteins were all coprecipitated by a neutralizing monoclonal antibody and were probably involved as target antigens in virus neutralization. Another antigenically unrelated glycoprotein with a molecular weight of 82,000 and a nonglycosylated protein with a molecular weight of 91,000 were also precipitated, but the immune response to these two proteins was transient. Reactivity to gp82 was only weakly detected in serum from naturally infected animals. Contact control animals which did not contract a bovine herpes virus type 1 infection but were exposed to infected animals with signs of severe illness had antibodies which recognized gp102, gp96, gp69 and gp55 as well as p115. These antibodies were present in low amounts and, in contrast to infected animals, did not increase between acute and convalescent sampling.