A simple theory of lung elasticity and its interaction with bronchi was developed which led to the specific results. The experimental procedure for establishing these results used lobar bronchi from excised dog lungs, following Takishima, et al. ((1975) J. Appl. Physiol., 38: 875-881). First, we found a semi-direct technique for measuring Poisson's ratio (sigma) of lung parenchyma and the effect of lung parenchyma on bronchi (interdependence). Sigma was measured at 0.424 +/- 0.045; no correlation was observed between sigma and the elastic recoil pressure of the lung (PL). The interdependence increased with a corresponding increase in PL and reduced bronchial volume. Second, we predict that a relationship exists between the specific compliances of intact and excised bronchi, and the specific compliance of the surrounding parenchyma. We suggest that the parenchyma is more important than the bronchus itself in determining the specific compliance of the intact bronchi.