Abstract. Let X and Y be Banach spaces and F ⊂ BY * . Endow Y with the topology τF of point-wise convergence on F . Assume that T : X * → Y is a bounded linear operator which is (w * , τF ) continuous. Assume further that every vector in the range of T attains its norm at some element of F (that is, for every x * ∈ X * there exists y * ∈ F such that T (x * ) = |y * (T x * )|). Then T is (w * , w) continuous. The proof relies on Rosenthal's ℓ1-theorem. As a corollary to the above result, one obtains an alternative proof of James's compactness theorem that a bounded subset K of a Banach space E is relatively weakly compact provided that each functional in E * attains its supremum on K.