  Perturbative corrections to b->c transitions at zero recoil are considered in
the two-step matching scheme. The matching coefficient for the b->c currents
from the intermediate effective theory (between the scales m_b and m_c) to the
low-energy effective theory (scales below m_c) has been found with two-loop
accuracy. The next-to-next-to-leading logarithms has been summed in the leading
order in m_c/m_b. Higher-order corrections are estimated in the large-beta_0
limit.
