The chemical stability and toxicity of Te–As–Se (TAS) infrared fibers are investigated. These fibers are used for biosensing applications that involve direct contact with live cultivated human cells. It is shown that TAS fibers exhibit a small oxidation layer after extended exposure to air. This layer is highly soluble in water and easily removed. However, the TAS glass itself is stable in water over several days. While oxidized fibers release arsenate ions, which result in toxic effects to the cells, fresh or washed fibers show no toxic effects. A good correlation is shown between surface etching and the disappearance of toxicity.