The translational and rotational diffusion of poly(tetrafluoroethylene) latex in aqueous solutions of unbound sodium poly(styrenesulfonate) were measured by dynamic light scattering. Both quantities were affected by the viscosity of the poly(styrenesulfonate), which was itself a function of added salt. Adjusted for viscosity, the rotational diffusion decreased with added salt but did not depend on the polymer concentration in the range studied. This suggests that rotational diffusion of a probe particle can be used to sense the local ionic environment. Visual observations and static light scattering showed that salt-induced aggregation of the latex can be prevented or reversed by small amounts (several milligrams per milliliter) of sodium poly(styrenesulfonate).