We have designed and constructed a combined surface plasmon resonance-scanning force microscope instrument capable of providing simultaneous in situ information on the dynamic behavior of the refractive index and spatial characteristics of surfaces. These data show considerable potential for revealing new insights into interfacial phenomena. In this article, we describe the instrument in detail and provide a brief example of the results obtained when studying the hydrolytic degradation of a bioerodable polymer film [poly(orthoester)] exposed to an acidic environment. Analyses of the plasmon resonance and force microscopy data reveals the kinetics of the polymer degradation process and the heterogeneities in polymer distribution and degradation, respectively.