The interaction between 23 anticancer drugs and hydroxypropyl-beta-cyclodextrin (HP beta CD) was studied by reversed-phase charge-transfer thin-layer chromatography and the relative strength of interaction was calculated. HP beta CD formed inclusion complexes with 15 compounds, the complex always being more hydrophilic than the umcomplexed drug. The inclusion forming capacity of drugs differed considerably according to their chemical structure. The intensity of interaction significantly increased with increasing hydrophobicity of the guest molecule, demonstrating the preponderant role of hydrophobic interactions in inclusion complex formation.