The one-electron Douglas-Kroll approach, and perturbation theory including only the mass-velocity and Darwin terms, are used to compute the scalar relativistic contribution to the atomization energies of BS. Both approaches predict an approximately 0.7 kcal/mol reduction in the atomization energy. In combination with improved one-particle extrapolation techniques, this leads to a revised estimate for the heat of formation of gaseous boron, Delta H(f,0)degrees[B(g)] = 135.1 kcal/mol and Delta H(f,298)degrees[B(g)] = 136.3 kcal/mol, with error bars +/-0.75 kcal/mol or less.