Rabies: doubtful and discordant results in fluorescent antibody test.

By a fluorescent antibody test animal brain samples were examined for the rabies antigen. Two observers read the results. Doubtful, suspicious or weak results in the test were reanalyzed in a virus isolation test on the murine neuroblastoma cell line. From 37 samples estimated doubtful by the fluorescent antibody test, 17 were positive in the virus isolation test.