Effect of formaldehyde liberated from formalin on disinfection of the surface of a filtered air under positive pressure (FAPP) house and the surface of equipment placed in the house was studied. Escherichia coli, Staphylococcus aureus and avian adenovirus were used in this study as a indicator to evaluate degree of disinfection. Satisfactory degree of disinfection of the house and equipment was obtained when formaldehyde was liberated from 40 ml. of formalin per 1 m.3 capacity. Bacteria and virus used in the experiments, as well as air-borne organisms in the house, were perfectly inactivated by fumigation for 24 hours at the level of formalin mentioned above.