Evaluation of reliable experimental quantities characterizing the isolated strong polyelectrolyte chain in solution at low ionic strengths is a challenge for researchers working in polymer science and biophysics. A simple method for estimating the intrinsic viscosity as initial slopes of the lnηr and ηsp vs. c dependencies is discussed. Using several examples, we have demonstrated the adequacy of this estimated intrinsic viscosity. The results determined in salt free water solutions for homologous series of sodium poly(styrene-4-sulfonate) in 30-fold range of molar mass, as well as for the polyions with the persistence length of the corresponding bare chains differing 30 times are discussed. The “apparent intrinsic viscosities” of poly(styrene-4- sulfonate) samples at non-zero polymer concentration in salt-free solutions are compared with the directly measured intrinsic viscosities at different ionic strengths.