The dependence on frequency of the limiting value of strain, ΨL, for which linear Viscoelastic response occurs in eccentric rotating disks (ERD) flow is studied theoretically and experimentally. The theoretical investigations are based upon the general simple-fluid theory of Coleman and Noll. It is shown that according to this theory ΨL becomes independent of angular velocity, ω, at relatively high frequencies, whereas ΨL becomes inversely proportional to at sufficiently low frequencies. The results of previous investigations, based upon some special rheological models, are discussed. The behavior predicted by the simple-fluid theory is confirmed by experiments on polyisobutylene solutions.