Viscoelasticity of the vocal fold was assessed by analyzing the stress-strain relationship under several experimental conditions. The stiffness increased with greater tension of the vocal fold. Marked differences in the mechanical properties were noted between the "body" and the "cover" of the vocal fold, especially when tension was applied. Contraction of the thyroarytenoid muscle tended to make the vocal fold less stiff and more viscous. Dry vocal-fold mucosa was associated with greater stiffness. Submucosal injection of saline solution to simulate edema increased the stiffness and viscosity of the vocal fold.