For a nontrivial finite Galois extension L/k (where the characteristic of k is different from 2) with Galois group G , we prove that the Dress map 68081bee105843dd33dbf24bf17af" title="Click to view the MathML source">hL/k:A(G)→GW(k) is injective if and only if where α is not a sum of squares in k×. Furthermore, we prove that hL/k is surjective if and only if k is quadratically closed in L . As a consequence, we give strong necessary conditions for faithfulness of the Heller–Ormsby functor , as well as strong necessary conditions for fullness of .