The colligative properties of poly(propylene imine) dendrimers in methanol have been investigated with low-angle laser light scattering and vapor pressure osmometry. The molecular weights and second virial coefficients of the first five generations have been determined. The molecular weights. have been found to agree with the theoretically expected values. Effective radii have been obtained from the second virial coefficient, viscosity, and the partial specific volume. Both pair interaction;and: viscous state of the particles are considered in terms of effective volumes. The fifth generation shows the most pronounced hard-sphere interaction probably reinforced by Coulombic repulsion. The viscosity behavior of these dendrimers is Like nondraining spheres. All radii grow almost linearly with the generation number. Together with the exponential growth of their molecular weights, this excludes a power law dependence of molecular weight and radius; i.e., these dendrimers are not self-similar. This also explains the maximum in the viscosity.