The addition of alpha-, beta-, and gamma-cyclodextrins to tetrakis(4-sulfonatophenyl)porphine (TPPS4) and its manganese(II) and manganese(III) complexes is characterized by optical and magnetic resonance spectroscopy. Microscopic binding constants for the formation of the cyclodextrin-(MnTPPS4)-T-III complexes are found to be 2.7, 94, and 41 M(-1) for the alpha-, beta-, and gamma- complexes, respectively, assuming two identical binding sites that are noncompetitive. The formation of the cyclodextrin complex inhibits dimerization or polymerization of the porphyrins. The water proton nuclear magnetic spin-lattice relaxation rates are reported as a function of the magnetic field strength and the millimolar relaxivities for the cyclodextrin-(MnTPPS4)-T-III complexes are similar to those of the free (MnTPPS4)-T-III except at high magnetic fields where the rotational correlation times of the complex become important. However, the relaxivities for the cyclodextrin-(MnTPPS4)-T-II complexes are quite high and not well described by the standard theories for paramagnetic relaxation. The shapes of the magnetic relaxation dispersion profiles are not Lorentzian and are more nearly approximated by the weaker magnetic field dependence of a translational diffusion model. However, such a model cannot simply account for the high relaxivities found.