The potential dependent structure of underpotentially deposited lead on silver (111) and the initial stages of bulk lead deposition on the ad-layer have been studied using grazing incidence X-ray scattering. Measurements were made in-situ and under potential control. The close packed triangular lattice of lead formed by the underpotential deposition (at full monolayer coverage) is compressed 1.4% relative to bulk lead. This compressive strain increases linearly with applied potential until the onset of bulk deposition where the ad-layer is compressed 2.8%. Bulk lead is not deposited epitaxially on this template because of the large compressive strain. Instead, it grows as islands that have (111) texture but are randomly oriented in the plane of the substrate. After the deposition of approximately five equivalent monolayers of bulk lead, the initial ad-layer appears to reconstruct. © 1989.