  For several processes at colliding beams, macroscopically large impact
parameters give an essential contribution to the standard cross section. These
impact parameters may be much larger than the transverse sizes of the colliding
bunches. In that case, the standard calculations have to be essentially modify.
The corresponding formulae for such a beam-size effect were given twenty years
ago without taking into account correlations of particle coordinates in the
beams. In the present paper we derive formulae which necessary to take into
account quantitatively the effect of particle correlations in the spectrum of
bremsstrahlung as well as in pair production. Besides, we consider critically
recent papers of Baier and Katkov [Phys. Rev. D {\bf 66}, 053009 (2002) and
hep-ph/0305304] in which it was calculated a new additional ``subtraction
term'' related to the coherent contribution into beam-size effect. We show that
this result is groundless and point out the origin of the mistake.
