  We discuss the general properties of the $B$-meson decay form factors
$F(q^2,q'^2)$, describing $B$-meson decays induced by two currents, e.g.,
$B$-decays into four leptons in the final state. We study the analytic
properties of these complicated objects and identify those regions of $q^2$ and
$q'^2$, where perturbative QCD can be applied for obtaining predictions for the
physical form factors.
