This paper attempts to illustrate how the porous nature of ice crystals might influence the relationships between the radiative properties of ice clouds and the ice water path. Solutions of the electromagnetic wave equation were obtained for a simplified, hollow, infinitely long circular cylinder. On the basis of these solutions it was implied that the effects of ice crystal porosity on the particle-scattering parameters can be expected to be small and that the major influence of porosity on radiation--ice water path (IWP) relationships will be primarily on the definition of IWP. It is suggested that this effect probably accounts for the existing discrepancy noted in this paper between the theoretical and observed &egr;-IWP relationships. ¿American Geophysical Union 1987