The physical and dynamical propel-ties of sodium chloride, guanidinium chloride, urea, and 2,2,2-trinuoroethano1 solutions have been investigated as a function of cosolvent concentration using molecular dynamics simulations. Properties studied included: solution densities, radial distribution functions and coordination numbers, diffusion constants, residence and reorientational times, and dielectric properties. In most cases, the observed trends in the experimental data as a function of increasing concentration were well reproduced, However, quantitative agreement with experiment was relatively poor, with most cosolvent effects being exaggerated in the simulations. The results highlight significant differences as well as similarities between the effects of guanidinium chloride and urea cosolvents. Aggregation of 2,2,2,-trifluoroethanol molecules in water at higher concentrations was also observed, in agreement with experiment.