Abstract: Background. Reduction of biofilm formation on tracheoesophageal voice prostheses by certain dairy products might extend their clinical lifetime. The purpose of this study was to determine the influence of certain dairy products on voice prosthetic biofilms and lifetimes in vitro and in vivo. Methods. The in vitro results were accomplished using an artificial throat. The lifetimes of Provox2 prostheses were evaluated in a patient group that daily consumed the evalu-ated products. Results. Buttermilk and Yakult Light fermented milk de-creased the amount of bacteria on voice prostheses but stimu-lated yeast prevalence in vitro. Concurrently, lifetimes of voice prostheses in patients consuming buttermilk were not signifi-cantly differ...