The results of immunofluorescent (IF) and immunoperoxidase (IP) technics applied for the detection of antigen in cerebrospinal fluid (CSF) cells in patients with mumps, herpes zoster and herpes simplex meningitis and meningoencephalitis are presented. Thirty patients were under study. The detection of mumps and herpes zoster viral antigen in CSF cells was possible in 100% of cases investigated. Herpes simplex virus antigen was detected in four of seven cases with symptoms of severe meningoencephalitis. Complement fixation (CF) antibodies to herpes simplex virus (type I) and positive seroconversion were detected in the four latter patients. The diagnostic value of the methods used for the detection of mumps, herpes simplex and herpes zoster viral antigens in CSF cells of patients is discussed.