Noncytopathogenic (NCP) bovine viral diarrhea (BVD) disease agents can be detected and titrated in tissue culture systems by a method employing immunofluorescence. Cytopathogenic (CP) and NCP viruses cross react with fluorescein-conjugated serum globulins produced against either CP and NCP viruses, but the fluorescence is more intense in the homologous system. Serum neutralization titers of sera against both CP and NCP groups were compared for both groups of viruses, and results of cross reactions were in agreement with results from immunofluorescence tests. Results of these two tests were discussed as to possible antigenic groupings of CP and NCP viruses. Use of immunofluorescence as a diagnostic test for BVD and as an alternate method of titrating NCP viruses in tissue culture systems is proposed.