The antimicrobial activity of essential oils in the gaseous state was evaluated in a closed system using an airtight box. The gaseous activity was expressed by a minimum inhibitory dose (MID) per unit space that allowed no microbial growth after incubation. The MID values of seven oils determined against bacteria and fungi revealed that most oils were more active against filamentous fungi than against bacteria or yeasts. Gaseous essential oils inhibited three stages of the life cycle of filamentous fungi: germination of a conidium, elongation of vegetative mycelium, and sporulation of reproductive mycelium. Perilla and thyme oils exhibited therapeutic efficacy against experimental tinea pedis in guinea pigs and gaseous citron oil extended the survival time of mice exposed to fatal candidiasis.