A semiempirical model of a pressure-area relationship for the bronchial airways is developed. It is described by a single similarity law consistent in form with the nonlinear elastic behavior of biological tissue. The tethering effect of the parenchyma is lumped into the wall properties of the bronchi and is included in an effective wall stiffness. The model, which is fitted to the experimental data of Takishima and his associates (J. Appl. Physiol. 38: 875-881, 1975), is lung-volume dependent and is therefore suitable for the analyses of airflow at different lung volumes, especially for modeling of forced expiration.