Sodium poly(isoprenesulfonate) (NaPIS) fractions consisting of 1,4- and 3,4-isomeric units (0.44:0.56) and ranging in molecular weight from 4.9 X 10(3) to 2.0 X 10(5) were studied by static and dynamic light scattering, sedimentation equilibrium, and viscometry in aqueous NaCl of a salt concentration (C-s) of 0.5-M at 25 degreesC. Viscosity data were also obtained at C-s = 0.05, 0.1, and 1 M. The measured z-average radii of gyration (1/2)(z) intrinsic viscosities [eta], and translational diffusion coefficients D at C-s = 0.5-M showed that high molecular weight NaPIS in the aqueous salt behaves like a flexible chain in the good solvent limit, On the assumption that the distribution of 1,4- and 3,4-isomeric units in the NaPIS chain is completely random, the [eta] data for high molecular weights at C-s = 0.5 and, 1 M were analyzed first in the conventional two-parameter scheme to estimate the unperturbed dimension at infinite molecular weight and the mean binary cluster integral. By further invoking a coarse-graining of the NaPIS molecule, all the [eta] and D data in the entire molecular weight range were then analyzed on the basis of the current theories for the unperturbed wormlike chain combined with the quasi-two-parameter theory. It is shown that the experimental (z), [eta], and D are explained by the theories with a degree of accuracy similar to that known for uncharged linear flexible homopolymers.