Let G(x) be the Green
function in a domain Ω ⊆ ℝm with a fixed pole, and Γ be an (m − 1)-dimensional
hyperplane. We give conditions on Ω and Ω ∩ Γ so that |∇G| is A∞ with respect to
the (m − 1)-dimensional measure on Ω ∩ Γ. Certain properties of the Riemann
mapping of a simply-connected domain in ℝ2 are extended to the Green function of
domains in ℝm.