Candida species have the propensity to colonize and erode into the surface of silastic causing a loss of function. Colonization of silastic tracheo-oesophageal speaking-valves is an important cause of valve failure post-laryngectomy: the exact nature of the colonization is unknown and light microscopic studies have not been reported previously. Microbiological examination of scrapings taken from the colonized oesophageal surface of failed speaking valves was arranged before sectioning for light microscopy. Conventional ultrathin sectioning of silastic was difficult, therefore 15 micrometre sections were cut after cooling the material to -30 degrees C. These sections were then stained with toluidine blue; Candida species taking up the stain. Microbiological examination of the colonies confirmed the predominance of Candida species in the biofilm. Light microscopy of the 15 micrometer sections revealed that the Candida colonies had invaded the silastic. This work demonstrates that the colonization of the silastic valve prosthesis in the oesophageal area is due predominantly to Candida species which actively invade the structure of the silastic. This is an important cause of speaking-valve failure post-laryngectomy.