The transformation from pseudomorphic to dislocated and back to pseudomorphic growth with increasing coverage is reported for molecular beam epitaxy of Ag on Pt(111). Below a critical size of 200 Angstrom two-dimensional Ag islands grow coherently strained, while larger islands relieve strain through the introduction of misfit dislocations. Upon completion of the first monolayer, the dislocations disappear and the Ag film again adopts a pseudomorphic structure. With the help of effective-medium theory calculations, it is shown that this effect is related to the elevated chemical potential of Ag adatoms on top of the first Ag monolayer. (C) 1997 Elsevier Science B.V.