Twelve samples of sodium hyaluronate ranging in weight-average molecular weight from 3.8 x 10(3) to 3.5 x 10(5) have been studied by static light scattering, sedimentation equilibrium, and viscometry with 0.5 M aqueous sodium chloride at 25 degrees C as the solvent. Viscosity measurements have also been made at 0.2 M NaCl. Intrinsic viscosity ([eta]) data confirm Cleland’s early conclusion that the polysaccharide chain in 0.2 or 0.5 M aqueous NaCl has an unmistakable semiflexibility but undergoes appreciable excluded-volume effects unless the molecular weight is low. It is found that the molecular weight dependence of [eta] in the aqueous salts is described almost quantitatively by the combination of the Yamakawa-Fujii-Yoshizaki theory for [eta] of an unperturbed wormlike chain and the Yamakawa-Stockmayer-Shimada (YSS) theory for excluded-volume effects when the Barrett function is adopted for the viscosity expansion factor. The radii of gyration obtained for the four highest molecular weight samples in 0.5 M aqueous NaCl are also explained consistently by the YSS theory with the Domb-Barrett function for the radius expansion factor. The persistence lengths determined are 4.2 and 4.1 nm in 0.2 and 0.5 M aqueous NaCl, respectively, and the molar mass per unit contour length is 400-405 nm(-1) in the aqueous salts.