The transfer of polarized radiation in a medium containing size-shape distributions of randomly oriented nonspherical particles is modeled by employing a prolate spheroidal particle model. The parameter characterizing the mean departure from sphericity of the shape-distribution is the effective aspect ratio of the particle ensemble. The radiance, the degree of linear polarization and the degree of circular polarization are strongly sensitive to a variation of the effective aspect ratio. This shape-sensitivity is observed consistently from size-shape distributions containing mainly moderately aspherical particles to those containing predominantly highly aspherical particles. When the effective aspect ratio varies between 4 and 12, the degree of linear polarization changes by as much as 0.15. At certain angles from the sun, the radiance changes by as much as 60% within the same range of effective aspect ratios. ¿ 1998 American Geophysical Union