This research investigates a promising antiviral compound based on polyprenols from Siberian silver fir (Abies sibirica). The physico-chemical characteristics of a preparation developed in aerosol form and an estimation of its protective efficacy against aerosol challenge of laboratory animals are presented. It is shown that (1) by using a simple ultrasonic disperser one can obtain aerosol of three formulations studied with about 70% of its mass accumulated in the size range below 1.8 microm; (2) 40-100% of aerosol particles contain preparation for different formulations; (3) after delivering under specified schedules, the preparations as developed can protect up to 100% of mice against 5 LD(50) of influenza A/Aichi/2/68 (H3N2) virus aerosol infection. Animals inhaled twice the preparation doses (which were 100 times lower than injection ones of the same efficacy) and did not exceed 10 microg/mouse. It was shown that the mode of action of this immunomodulating preparation was nonspecific stimulation of immune cells' various activities.