Specific high-titre bovine conjugated antisera were obtained against respiratory syncytial virus. Use was made of the reference strain Nomi and the local isolate Antonovo/448. The conjugates produced were shown to have equal qualities to those of the Belgian conjugate used for comparison. The anti-Antonovo/448 conjugated serum was used in the direct immunofluorescent method to demonstrate a respiratory syncytial virus antigen in organs of animals with acute respiratory diseases as well as to control the replication of the virus in cell cultures. An infection with a respiratory syncytial virus was demonstrated with the employment of the same test in 16 per cent of a total of 119 samples taken from diseased animals. In the inoculation of the diploid cell culture of lamb thyroid gland with strains of the virus a specific antigen was established at the forty-eighth to the seventy-second hour following infection.