The incorporation of a homologous series of alkyl p-hydroxybenzoates into beta-cyclodextrin was studied by diffusion measurements. In some cases, all the anionic species and the larger neutral solute, butyl p-hydroxybenzoate, the occurrence of two species with different diffusion coefficients was observed, as CD concentration increased. Based on their derived hydrodynamic radii, these species were ascribed to 1 : 1 and 1 : 2 (solute:CD) complexes. The interaction of the neutral, mono and bianionic species of p-hydroxybenzoic acid with beta-CD was also investigated, but, in this case, only 1 : 1 complexes were observed. The strength of solute-CD interaction was estimated from the observed decrease in diffusion coefficients at higher CD concentrations and no significant effect was verified within the homologous series that could be ascribed to hydrophobic effects. A smaller extent of interaction was estimated for the anionic species, possibly due to the contribution from electrostatic repulsion with ionised CD hydroxyl groups. These results prove the potential of diffusion measurements as an invaluable tool in assessing complex stoichiometry and in providing insights in the incorporation process.363267277