A poly(hydroxyethylamino)- and a poly(sulfonatophenyloxy)--cyclodextrin derivative, bearing opposite ionic charges, have been shown by potentiometric titration to form stable pH-dependent heterodimers with each other in water. The formation constants of these dimers show that a very stable assembly is formed between the fully deprotonated sulfonato derivative and the fully protonated amino derivative (log K_a = 8.5), which constitutes the assembly of multiple extended atomic groupings on cyclodextrin as template.