  Denote by $M_n$ the algebra of $n\times n$ matrices. We consider the dyadic
paraproducts $\pi_b$ associated with $M_n$ valued functions $b$, and show that
the $L^\infty (M_n)$ norm of $b$ does not dominate $||\pi_b||_{L^2(\ell
_n^2)\to L^2(\ell_n^2)}$ uniformly over $n$. We also consider paraproducts
associated with noncommutative martingales and prove that their boundedness on
bounded noncommutative $L^p-$% martingale spaces implies their boundedness on
bounded noncommutative $L^q-$% martingale spaces for all $1<p<q<\infty $.
