Nine hyaluronan (HA) samples were fractionated by size-exclusion chromatography, and molar mass (M), radius of gyration (R-g), and intrinsic viscosity ([eta]) were measured in 0.15 M NaCl at 37degreesC by on-line multiangle light scattering and viscometer detectors. Using such method, we investigated the R. and [eta] molar mass dependence for HA over a very wide range of molar masses: M ranging from 4 x 10(4) to 5.5 x 10(6) g/mol. The R-g and the [eta] molar mass dependence found for HA showed a meaningful difference. The R-g = f(M) power law was substantially linear in the whole range of molar masses explored with a constant slope of 0.6. In contrast, the [eta] = f(M) power law (Mark-Houwink-Sakurada plot) showed a marked curve shape, and a linear regression over the whole range of molar masses does not make sense. Also the persistence length (stiffness) for HA was estimated. The persistence length derived by using both the Odijk's model (7.5 nm from R-g vs M data) and the Bohdanecky's plot (6.8 nm, from [eta] vs M data) were quite similar. These persistence length values are congruent with a semistiff conformation of HA macromolecules.