Intracordal injection therapy is a surgical therapeutic modality for glottic incompetence caused by unilateral laryngeal paralysis. Atelocollagen, which has recently been attracting attention as a material for use in intracordal injection therapy that supplants silicon, was initially claimed and expected, by virtue of its salient biophysical properties, not to cause impaired wave-motion of the vocal mucosa when injected into the submucosa. Unfortunately, however, our attempt to use this material for the same purpose proved disappointingly unsuccessful, with vocal sounds produced thereafter being metallic, vocal folds becoming tense and consequently transforming the site into a muscular coat of vocal muscles. During the past 3 years, we at the Department of Otolaryngology of the Jikei University School of Medicine, have performed intracordal injection therapy with atelocollagen on 20 patients diagnosed as having unilateral laryngeal paralysis under local anesthesia using a flexible fiberscope and a stroboscope under a video monitoring system. Comparisons were made of the voice before and after injection in 6 patients receiving submucosal injection and 14 given intramuscular injection of the material. In some autopsied patients, histological findings of the treated vocal cords were scrutinized and problems regarding atelocollagen injection were investigated. Judging from pathological findings of the vocal cords after atelocollagen injection and the clinical results of this therapeutic procedure, it seems most appropriate to inject this plastic material into the vocal muscles. This will prevent atelocollagen diffusion and maintain unimpaired wave-motion of the vocal mucosa, thus resulting in an acceptable voice quality.