One male subject was used as test person in anin vivo-study of oral films formed on well defined germanium prisms under unprovoked oral conditions as well as in the presence of sucrose or blood. The following analytical techniques were performed on the adsorbed films: a. internal reflection infrared spectroscopy, b. ellipsometry, c. scanning electron microscopy and d. energy-dispersive x-ray analysis.The results show that in the created moderately stagnated intraoral system the formation of biological films was similar in different parts of the oral cavity. The process was not found to be markedly influenced by the presence of blood. Sucrose, on the other hand, was found to increase both the overall film thickness and the carbohydrate-content of the films.The attachment of microorganisms was found to be a process proceeding at a comparatively slow rate especially in the presence of sucrose and when compared with biological debris. The majority of the first adhering microorganisms were found to be rod-shaped.