Using scanning tunneling microscopy (STM), we have imaged individual molecules of copper phthalocyanine absorbed on polycrystalline silver surfaces under UHV conditions. In addition to observing molecules on stable adsorption sites at atomically rough regions, we find evidence for surface diffusion during scanning over molecules adsorbed on flat areas of the sample. The role of applied electric field on the stability of the STM images and molecular bonding to the substrate is discussed. We tentatively suggest possible mechanisms for the tunneling process. © 1987.