Results of an in situ scanning-tunneling microscopy (STM) study on the initial stages of Ni electrodeposition on Ag(111) are presented and compared with previous results on Au(111). In the submonolayer range the STM results indicate substantial place exchange of Ni with Ag surface atoms. Submonolayer Ni islands are formed almost exclusively at the step edges, they are partly embedded into the upper terrace. in contrast, on Au(111) place exchange of Ni adatoms with the Au substrate occurs exclusively at the elbow sites of the herringbone reconstruction, and adlayer nickel islands nucleate selectively on top of the embedded Ni atoms (low overpotential) or also at steps (high overpotential). At multilayer coverages atomically smooth Ni deposits are found on both metal substrates with a lattice constant similar to that in metallic Ni, On Ag(111) large, quasi-two-dimensional Ni islands are observed, contrasting the almost perfect layer-by-layer growth on Ni/Au(111). The density of structural defects within the Ni islands on Ag(111) is significantly lower than for the Ni film on Au(111).