A general description of the electrolytic cond. behavior of highly charged strong polyelectrolytes in dil. and semidilute aq. solns. is presented. For the first time this model considers the effects of the molar mass, charge d. (for charge distances less than the Bjerrum length), polyelectrolyte concn., and the ionic strength adjusted by both the polyelectrolyte concn. (cp in monomol L-1) and added simple salt concn. (cs in mol L-1). Above the overlap concn. (c*) the molar mass influence is weak; below c* the equiv. cond. (L) increases strongly when cp decreases (cp > cs). The following relations were found: Lmax .apprx. cs-1/5 and Lmax .apprx. M-2/5 (M is molar mass). The cond. behavior can be qual. explained in terms of Manning's theory with an addnl. change of the interaction parameter fc. An empirical dependence of fc on the ratio of the Debye length to the contour length (lD/L) was found. Three concn. regimes differing in the polyion-counterion interaction were identified; these are characterized by the conditions: (lD/L < 4p)-1/2, (4p)-1/2 < lD/L < 1, and lD/L > 1, resp. The model describes polyelectrolyte solns. characterized by arbitrary (including zero) salt concn. [on SciFinder (R)]