The most important problem of the useful life of vocal prostheses is bacterial and especially mycotic colonization of their surface which impaired tightness of the closing valve of the prosthesis and caused subsequent leakage of fluids and food into the airways. The objective of the present study was to prevent colonization of the silicone surface and to prolong the service life of the prosthesis. The implanted prostheses were examined under microscope after varying intervals in vivo. The silicone of the implanted prosthesis was colonized by numerous microorganisms, in particular moulds. Seventeen bacterial and mycotic strains were identified. They behave to Candida, Acinetobacter, Micrococcus, Pseudomonas, Bacillus and Chryseomonas. The results confirmed the deep degradation of silicone rubber located in islets. Plant of bacterial tissue were inoculated on two types of silicone disks. Two types of silicone were tested (Silastic Q7-4550-50ShA and Q7-4765-65) after 4, 8 and 12-week exposure. Neither of these materials was attacked by mycotic agents in vitro. Only frame print was appreciable in five hundred times magnification. The second object of the study was to recognize the main degradation factor that means a kind of microorganism. The ability of microorganisms to assimilate oligo- and polyorganosiloxans was studied. Candida albicans does not seem like a typical microorganism assimilating silicon rubber. The results of our study proved Microccus as a typical vector which assimilates silicone.