  Let $M$ be the moduli space of complex Lagrangian submanifolds of a
hyperK\"ahler manifold $X$, and let $\varpi : \widehat{\mathcal{A}} \rightarrow
M$ be the relative Albanese over $M$. We prove that $\widehat{\mathcal{A}}$ has
a natural holomorphic symplectic structure. The projection $\varpi$ defines a
completely integrable structure on the symplectic manifold
$\widehat{\mathcal{A}}$. In particular, the fibers of $\varpi$ are complex
Lagrangians with respect to the symplectic form on $\widehat{\mathcal{A}}$. We
also prove analogous results for the relative Picard over $M$.
