Multiple internal reflection spectroscopy, a very sensitive technique, has been used in the past to characterize deposits from various environments (such as the oral cavity), on internal reflection elements such as germanium. To understand the surface interactions with real surfaces (such as the apatitic tooth surface or stainless steel heat exchange surfaces), the use of appropriate methods to deposit thin films of the substrata of interest, on suitable internal reflection elements, is suggested. This permits the application of multiple internal reflection spectroscopy, to characterize the deposits formed on various types of real surfaces. This approach is illustrated by depositing a thin, solid film of hydroxyapatite (a multicomponent compound which forms the major constituent of the outermost part of the tooth surface) on germanium internal reflection elements, by radiofrequency sputtering. The chemical composition and molecular structure of the films deposited under suitable conditions were very close to those of the bulk material. The adsorption of salivary components on these sputter coated internal reflection elements could be detected by multiple internal reflection infrared spectroscopy.