  We analyze the fully relativistic, field-theoretical treatment of the scalar
Coulomb problem. We work in a truncated Hilbert-Fock space containing the
two-constituent states and the
two-constituent-and-one-massless-exchange-particle states. Self-energy
contributions are dominant for large values of the coupling constant. Using the
covariant formulation of the self-energy does not alter these results
significantly. Both the weak-coupling limit and the heavy-mass limit lead to
the non-relativistic results.
