Diffusion-ordered 2D NMR spectroscopy (DOSY) has been used to study the non-Newtonian to Newtonian transition in a hexadecyltrimethylammonium bromide (CTAB)/sodium salicylate/water viscoelastic micellar system induced by the addition of a slightly hydrophobic and yet water-soluble polymer. The change in the size of the surfactant aggregates upon the addition of polymer, the binding of the salicylate ions to the micellar aggregates, and the interaction between the polymer molecules with the micellar aggregates are revealed by the diffusion coefficients of the constituents as a function of the amount of polymer, poly(vinyl methyl ether), added into the system. It is concluded that the addition of the polymer reduces the aggregate size. When a sufficient amount of polymer is present in the system and at slightly elevated temperature (30-40 degrees C), the long rod micelles in the viscoelastic system are broken up into relatively small, and probably spherical, micelles. Strong correlation of the diffusion of the polymer and surfactant aggregates is also present under this condition.