The positional-orientational probability distribution function of a number of hard-body biaxial solute particles, treated in the Zwanzig approximation and dissolved in the smectic A phase of parallel hard spherocylinders, has been calculated using a second-virial theory. It is found that the tendency of a solute to be partitioned between intra-and inter-layer regions, each one associated with a different degree of solute orientation, exhibits a non-monotonic behavior with the geometrical parameters defining its shape and size. These results, compared with the available experimental and numerical data. could be of help in qualitatively interpreting ordering phenomena of interest in both material and biological sciences. (c) 2005 Elsevier B.V. All rights reserved.