The process includes a treatment step during which a liquid containing a biocidal and/or plant-protection product or a mixture of biocidal and/or plant-protection products is evaporated and injected into the internal atmosphere of premises, the liquid being evaporates at a temperature of less than 50° C., the product vapour concentration in the internal atmosphere of the premises being kept at greater than 10% of a saturation concentration of the vapour of said product in said atmosphere at said temperature for a saturation duration of greater than 12 hours.
