  We characterize the symbols of Hankel operators that ex- tend into bounded
operators from the Hardy-Orlicz $H^{\Phi_1} (\mathbb B^n)$ into $H^{\Phi_2}
(\mathbb B^n)$ in the unit ball of Cn, in the case where the growth functions
$?\Phi_1$ and $\Phi_2$ are either concave or convex. The case where the growth
functions are both concave has been studied by Bonami and Sehba. We also obtain
several weak factorization theorems for functions in $H^\Phi(\mathbb B^n)$,
with concave growth function, in terms of products of Hardy-Orlicz functions
with convex growth functions.
