Chiral recognition of Ru(phen)(3)(2+) (phen = 1,10-phenanthroline) by heptakis(6-carboxymethylthio-6-deoxy)-beta-cyclodextrin heptaanion (per-CO2--beta-CD) in D2O has been studied by means of H-1 NMR spectroscopy. The binding constant for the Delta-Ru(phen)(3)(2+) complex (K = 1250 dm(3) mol(-1)) is about 2.1-times larger than that for the Lambda-isomer (Delta Delta G = 1.9 kJ mol(-1)). A clockwise helix-configuration of the Delta-isomer may well fit to the asymmetrically twisted CD cavity.