Light-scattering spectroscopy was used to examine diffusion of optical probes of various radii in solutions (0 less than or equal to c less than or equal to 15 g/L) of 300 kDa hydroxypropylcellulose (HPC) at 25 degrees C. Spectra follow well a stretched-exponential g((1))(t) = A exp(-theta t(beta)) = A exp((t/tau)(beta)), plus at elevated c a weak, rapid initial decay. Accurate values for theta, beta, and tau were obtained via multi-tau spectral splicing techniques. For 109, 189, and 760 nm diameter spheres, theta eta (eta is the solution viscosity) is independent of c. HPC:water shows pseudo-Stokes-Einsteinian behavior for large probes. For 21 nm probes, theta eta increases by 10-fold over 0 less than or equal to c less than or equal to 15 g/L. From the eta and scattering vector dependences, theta and beta are inferred to be the quantities most likely to be amenable to direct theoretical calculation.