In spite of the fact that film theory is based on severe assumptionss, it is shown to be a good working model. The Niebergall-Goyan equation, the Short-Sharkey-Rhodes equation, and the Pothisiri-Carstensen equation-all based on simple film theory-are shown to hold through 80-90% of the dissolutin process for p-hydroxybenzoic acid and sodium chloride, both at values below and above the amount necessary to saturate the dissolution medium. Deviations are attributed to experimental difficulties and to improper definition of monodisperseness rather than to the assumptions made in the theory.