The forces between a tungsten tip and a self-assembled monolayer of hexadecylthiol (C16H33SH) on a thin gold film have been studied using a newly developed interfacial-force microscope. Imaging of the surface, combined with spatially resolved force versus separation measurements, allow for the distinction of topographical and chemical features of the surface. Several distinct regions are observed for this system. The first, characterized by a very weak interfacial interaction between tip and sample, is representative of the self-assembled monolayer. The other regions show relatively strong, long-range attractive forces, which are associated with gross defects in the film.