  Based on the QCD factorization approach we analyse the branching ratios for
the channel $B \to \rho \pi$. From the comparisons with experimental data
provided by CLEO, BELLE and BABAR we constrain the form factor $F^{B \to
\pi}(m_{\rho}^{2})$ and propose boundaries for this form factor depending on
the CKM matrix element parameters $\rho$ and $\eta$.
