In processes involving Coulomb-type initial- and final-state interactions,
the Gamow factor has been traditionally used to take into account these add
itional interactions. The Gamow factor needs to be modified when the magnit
ude of the effective coupling constant increases or when the velocity incre
ases. For the production of a pair of particles under their mutual Coulomb-
type interaction, we obtain the modification of the Gamow factor in terms o
f the overlap of the Feynman amplitude with the relativistic wave function
of the two particles. As a first example, we study the modification of the
Gamow factor for the production of two bosons. The modification is substant
ial when the coupling constant is large.