Ventilation systems often host bacteria and fungi that may be dangerous for the health of exposed people. Essential oils are one means among others to prevent microbial development. Used as a basis for many traditional therapies, these odorant plant extracts have been studied extensively in the medical domain and their effectiveness in the treatment of numerous pathologies has been demonstrated. As opposed to most antimicrobial agents currently used for air disinfection, essential oils are not toxic. With a view to proposing an indoor air purification method based on the germicidal and odorant properties of essential oils, we selected: the pathogenic test strains : Staphylococcus aureus and Pseudomonas aeruginosa the Afnor NF T72-281 protocol for the disinfection of surfaces through the air, which showed the germicidal activity of antimicrobial agents used in gaseous phase a specific experimental apparatus some of the most active essential oils : mountain savory, thyme thymol, oregano (vulgare) as well as cinnamon bark. The protocol was applied to a chemical reference compound of hospitals, the formaldehyde as well as to phenol rich essential oils. We demonstrated that the tested essential oils in gaseous phase do have a lethal effect on all bacteria that have been exposed to them, even in small doses. In buildings, controlled diffusion of rigorously selected essential oils in volatile form would validly contribute to: occupant comfort, through improvement of the perception of indoor air quality, the prevention of microbial contamination, microbiological purification of air and sanitation of ventilation systems.