  Let $k$ be a field of characteristic zero, $\g$ a $k$-Lie algebra,
$e:S\g@>>>U\g$ the symmetrization map. The PBW quantization is the one
parameter family of associative products: $$ x\star_t y=\sum_{p=0}^\infty
B_p(x,y)t^p\qquad (t\in k) $$ where $B_p$ is the homogeneous component of
degree $-p$ of the map $B:S\g\otimes_kS\g@>>>S\g$, $B(x,y)=e^{-1}(exey)$. In
this paper we give an explicit formula for $B$. As an application, we prove
that for each $p\ge 0$, $B_p$ is a bidifferential operator of order $\le p$.
