We have investigated the linear viscoelastic properties of high molecular weight hyaluronan in aqueous solution using an experimental approach combining mechanical rheometry and optical microrheology. The complex shear modulus has been measured over a broad frequency range from 10(-1) to 10(7) rad/s. Chain flexibility is characterized by the persistence length l(p) and this parameter has been determined for the first time in the entangled regime here from high frequency modulus data. At NaHA concentrations above the entanglement concentration c(e), l(p) is essentially independent of polymer concentration, temperature, and ionic strength. The latter is consistent with the Odijk-Skolnick-Fixman theory. The scaling exponent describing the concentration dependence of the plateau modulus G(0) agrees well with predictions for polymers in good solvents. The scaling exponents for the specific viscosity eta(sp) and relaxation time T-R are slightly higher than theoretically predicted for polyelectrolytes in the high salt limit, indicating, that molecular aggregation occurs at higher polymer concentrations.