Bc mass up to order αs4 -: art. no. 094019

We evaluate in perturbative QCD, up to order alpha (4)(s) the mass of the B-c. We use the so-called 1S mass in order to improve the convergence of the perturbative series. Our result is E(B-c)(pert) = 6326(-9)(+29) MeV. Nonperturbative effects are discussed. A comparison with potential models seems to be consistent with nonperturbative contributions of the order - (40-100) MeV.