Particle orientation in particleboard was characterized by two directional distribution functions, the von Mises and truncated gaussian. This approach has the advantage of characterizing the degree of orientation by specifying only one parameter. A method was developed to measure the orientation of particles in particleboard "in situ", and to express the orientation in terms of the direction distribution functions. Models were developed to compute the tensile and shear modulus of particleboard with various degrees of orientation. The tensile model worked well for several board types. The shear model, however, was only effective for thin plates. Poisson's ratio, the tensile modulus, modulus of elasticity, and modulus of rupture increased in the direction of particle alignment as the degree of orientation increased. The shear modulus decreased as the orientation increased. The results indicate that conventional methods of orienting particles must be greatly refined before the potential benefits of orientation are realized. / Ph. D.