[en] Adopting the Bethe-Salpeter formalism for the treatment of hadrons the relative contributions of the two-quark annihilation and three-quark fusion mechanisms to baryon number violating nucleon decay are compared. The former is found to dominate over the latter by a factor of about 3 in amplitude, implying a proton lifetime of 4 x 1030 yr for msub(X) = 4.2 x 1014 GeV. (Author)