This electron microscopic investigation was performed to examine the ultrastructure of the in vivo formed salivary pellicle on 15 different dental materials. Test pieces of amalgam alloys, casting alloys, titanium, ceramics, resins, composite resins, glass polyalkenoate cement, and bovine enamel were attached to the buccal and lingual surfaces of the upper first molars in three adults using removable intraoral splints. The splints were carried over periods of 2 and 6 h. Pellicle-like structures could be identified on all tested material surfaces by transmission electron microscopic analysis. The pellicle layer showed a high degree of similarity on different kinds of surfaces with regard to the ultrastructural appearance. However, distinct differences could be detected in the ultrastructural pattern and thickness of the pellicle layer formed on buccally and lingually mounted specimens. Pellicles adsorbed on buccally carried test pieces were characterized by a heterogeneous, globular appearance and a thickness ranging from 500 to 1,000 nm after 6 h. In contrast, all lingually mounted test pieces were covered by a granular pellicle of about 100 nm thickness after 6 h. It is concluded that the ultrastructural pattern and extent of salivary pellicle formation are influenced by locally available salivary biopolymers and locally effective shearing forces rather than by material-dependent parameters.