Tested was the effect of the iodoform preparation iosan and the quaternary ammonium preparation bradofen against the viruses of the Newcastle disease (strain La Sota), laryngotracheitis (strain TsNIIP) and fowl pox (strain FK) in birds. The following results were obtained: 1. To a concentration of 3% (262 ppm of active iodine) and exposure of 45 min. to iosan the virus of laryngotracheitis was sensitive; that of Newcastle disease perished at a conc. of 5% (525 ppm of active iodine for 15 min); and that of fowl pox was not inactivated at a 30 min. exposure to a conc. of 7% (875 ppm of active iodine.) 2. Bradofen inactivated the Newcastle disease virus in a conc. of 0.5 per cent for 30 min., while the pox virus withstood a conc. of 1.5% up to the 30 th min. The virus of laryngotracheitis was inactivated by a conc. of 2 per cent for 45 min. The disinfection effect of the tested preparations was assessed as satisfactory.