The possibility of determining the association constant of a 1:1 charge-transfer complex AB in solution from the concentration dependence of the relaxation time is discussed. If small quantities of termolecular complexes A2B and AB2 are also present there will be two additional relaxation times corresponding to the decomposition rate constants of these complexes. It is shown that if A and B are aromatic molecules whose two sides act completely independently so as to form an infinite series of sandwich complexes (model 3), then the usual relaxation techniques would detect only one relaxation time whose concentration dependence would be indistinguishable from that of a system containing only one complex, AB. If such a system were mistakenly assumed to contain only one complex AB, relaxation methods would lead to the correct value for the dissociation rate constant of AB but to an association rate constant equal to half the true value. The association constant found would thus be equal to half its true value, just as if it had been determined spectrophotometrically. The complete relaxation spectrum of model 3 and the corresponding normal reaction coordinates were calculated; the reciprocal relaxation times form three infinite series, the spacing in each series being twice the dissociation rate constant of AB. If the rate constants of reactions involving isolated molecules of A or B differ slightly from those of the corresponding reactions involving complexes of A and B, then perturbation theory shows that in principle three relaxation times, instead of one, should be observable; in practice, difficulties would arise since these relaxation times are all of similar magnitude.