The dynamics of macromolecules in ternary solutions consisting of a probe polymer, a matrix polymer, and a solvent are studied using dynamic light scattering (DLS) with refractive index matching and, as supporting techniques, static light scattering and viscometry. The probe is linear polystyrene (PS) of molecular weight 390 000, which was always present in dilute amounts. The matrix polymer is poly(n-hexyl isocyanate) (PHIC) of varying molecular weight and polydispersity, whose concentration ranged from dilute to semidilute. The solvents used are either 1,1,2,2-tetrachloroethane (TCE) or toluene. PHIC is completely isorefractive in TCE at 75.0 degrees C. At lower temperatures and in toluene it is nearly isorefractive, removing the direct contribution of the PHIC to the lightscattering spectrum. DLS measurements of PHIC in chloroform show that the PHIC behaves as a wormlike chain with a persistence length of similar to 20 nm. Results from previous studies of PS in binary solution are used for comparison to its behavior in the ternary solutions, which contained varying amounts of PHIC. Ternary solution studies were conducted over a range of temperature from 25 to 75 degrees C. The translational diffusion coefficient of the PS in ternary solution decreases with increasing concentration of PHIC, but the overall dimension of the PS remains essentially constant for all solution conditions. The decrease in PS diffusion coefficient is smaller than that predicted by reptation. Comparison of the different fractions of PHIC shows that the translational diffusion coefficient of PS is affected by the flexibility of the PHIC. The PS diffusion coefficient for all the PHIC fractions depends on the end-to-end distance of the PHIC. A fast relaxational mode (not present in dilute PS solutions) was seen in the DLS spectra for samples above a certain onset concentration of PHIC. The amplitude of this relaxation is always a small portion of the DLS spectrum, ranging from 0 to 5% of the total intensity. Using the contour length of the wormlike chain for the apparent rod length gives an onset concentration for the fast mode of CL(3) similar to 10-15. The physical cause for this relaxation is unclear, although several possible explanations for it are discussed.