  Nonperturbative effects in exclusive reactions $B\to K^{(*)}ll$ are
discussed. Form factors which describe the main long-distance contribution to
the meson transition amplitude are calculated within the dispersion formulation
of the quark model: namely, the form factors in the decay region are expressed
as relativistic double spectral representations through the wave functions of
the initial and final mesons. The dilepton forward-backward asymmetry and the
lepton polarization turn out to be largely independent of the particular choice
of the quark model parameters and can be predicted with high accuracy. At the
same time, these asymmetries are sensitive to the short-distance structure of
the theory and might be used as a test of the Standard Model and probe of new
physics.
