Four narrow-distribution samples of sodium hyaluronate with weight-average molecular weights M-w of 3.8 x 10(3) to 1.1 x 10(4) in 0.02 and 0.1 M aqueous NaCl at 25 degrees C have been studied by small-angle X-ray scattering. Data for their z-average radii of gyration (1/2)(z) and particle scattering functions P(theta), together with previous (z) data from light scattering for high molecular weights, are compared with relevant theories for the wormlike chain with or without excluded volume, using the parameters estimated previously from intrinsic viscosity ([eta]) data. It is shown that for M-w lower than 1.1 x 10(4), (z), P(theta), and [eta] of the polysaccharide in the aqueous salts are all consistently explained by this model without excluded volume.