Solution studies of Cu2+ and Cu(en)22+ and Ni2+, Ni(en)2+, Ni(en)22+, and Ni(en)32+ in dimethyl sulfoxide (DMSO) were made. The kinetics of exchange of coordinated DMSO with DMSO bulk solvent were measured by NMR line broadening techniques. At low temperatures, axially coordinated DMSO molecules exchange from the six-coordinated Cu2+ with a rate constant of 4.7 × 103 sec-1 (25°C). However, the axially coordinated DMSO molecules on the Cu(en)22+ exchange at a rate too fast to be measured by the NMR line broadening technique. At higher temperatures, the exchange of DMSO molecules equitorially coordinated to Cu2+ was measurable and evidence for DMSO exchange from the partially dissociated Cu(en)2+ was observed. The average rates of exchange for DMSO molecules coordinated to Ni2+ and Ni(en)x complexes follow the order Ni2+ < Ni(en)2+ < Ni(en)22+. The increase in exchange rate upon successive addition of ethylenediamine can be explained by an amine trans effect. Conclusions drawn from the NMR line broadening results are supported by paramagnetic NMR chemical shift, solution magnetic susceptibility, and calorimetric data.