In the characterization of stress-strain relationships for the lung using solid continuum-mechanics analysis, the lung parenchyma is assumed to be in a state of uniform expansion and nonhomogeneous deformations are considered from the uniform state. If the nonhomogeneous deformations are small, nonhomogeneous lung deformation problems are reduced to those solvable using infinitesimal elasticity, since only the small superimposed deformations are considered. Using this incremental approach, the relevant elastic constants of lung parechyma have been measured and their applicability has been verified by comparing the results of the theoretical analysis of several nonhomogeneous deformation problems with experimental data.