  The dependences on z of fractional number densities of H+ and He+ ions are
calculated with a proper allowance for two-photon decays of upper levels of
hydrogen and parahelium and radiative transfer in intercombination line 2 3P_1
--> 1 1S_0 of helium. It is shown that for hydrogen this gives corrections for
a degree of ionization in no more than a few percents but for helium this leads
to a significant acceleration of recombination compared to the recent papers by
Seager et al. (1999; 2000) where these effects were ignored.
