Brummelhuis R., Siedentop, H., Stockmeyer, E. The Ground State Energy of Relativistic One-Electron Atoms According to Jansen and Hess (43K, LATeX) ABSTRACT. Jansen and He{\ss} -- correcting an earlier paper of Douglas and Kroll -- have derived a (pseudo-)relativistic energy expression which is very successfull in describing heavy atoms. It is an approximate no-pair Hamiltonian in the Furry picture. We show that their energy in the one-particle Coulomb case, and thus the resulting self-adjoint Hamiltonian and its spectrum, is bounded from below for $\alpha Z\leq 1.006$.