We have reexamined the role played by transient rheology in the interpretation of mantle viscosity. This investigation has been carried out by comparing the amplitude responses with the data of secular variation of, the relative sea‐level histories at sites well within the ice margins and at the ice margin like the city of Boston. A linear Burgers’ body rheology has been assumed in the lower mantle. The data near the edge of the ice load proves most sensitive to the transient viscosity structure. The non‐monotonic behavior of sea‐level data near Boston can be explained both by a steady‐state lower mantle viscosity of 1022P with a thick lithosphere and also by a transient lower mantle rheology but with a thin lithosphere. The long‐term viscosity of the lower mantle in this second model has a steady‐state value of around 5×1023P.