Control of postharvest diseases of fruits and vegetables by biocontrol agents applied under commercial conditions are sometimes less satisfactory than protection exerted by synthetic fungicides. We report some recent research aimed at enhancing and stabilizing the activity of selected yeasts by combining with various adjuvants. Several food-grade additives and antioxidants consistently enhanced the antagonistic activity of the biocontrol yeasts against postharvest fungal pathogens in small-scale experiments. Moreover, the activity of antagonists was significantly improved by combining with a low dose of synthetic fungicides on apples in semi-commercial conditions. The potential application of selected compounds and strategies for developing new formulations of yeast-based biofungicides are discussed.