We have been studying the index theory for some special infinite-dimensional manifolds with a "proper cocompact" actions of the loop group LT of the circle T , from the viewpoint of the noncommutative geometry. In this paper, we will introduce the LT -equivariant KK-theory and we will construct three KKelements: the index element, the Clifford symbol element and the Dirac element. These elements satisfy a certain relation, which should be called the (KK-theoretical) index theorem, or the KK-theoretical Poincaré duality for infinite-dimensional manifolds. We will also discuss the assembly maps.