The max. quantity of bulk Hg(0) which can exist on the surface of a Au electrode in acidic media corresponds to a coverage of theta sub Hg(0) = 1. Deposited Hg(0) in excess of this quantity diffuses into the Au substrate to form a bulk Au--Hg alloy; however, no alloy is formed until theta sub Hg(0) = 1. The potential for the stripping peak of the Au--Hg alloy is positive of the peak potential for the stripping of bulk Hg(0) by approx 0.4 V. The diffusion rate for Hg in the Au--Hg alloy is sufficiently slow so that the alloyed Hg is never totally stripped under the usual condition of cyclic voltammetry. Evidence is also given for the formation of Hg(I) adions during the underpotential deposition process for which n sub app = 1.6 eq mole exp --1 . 8 ref.--AA