Abstract. In this paper we describe the structure of all sequential isomorphisms between the sets of von Neumann algebra effects. It turns out that if the underlying algebras have no commutative direct summands, then every sequential isomorphism between the sets of their effects extends to the direct sum of a *-isomorphism and a *-antiisomorphism between the underlying von Neumann algebras.

AMS Subject Classification (1991): 46L60, 47B49

Received August 18, 2003. (Registered under 2929/2009.)