Two-dimensional electrophoresis was used to resolve approximately 162 polypeptides from the isolated oral apparatus of Tetrahymena thermophila. The molecular weight range was between 110 000 and 15 000 Daltons. The polypeptides had apparent isoelectric points between pH 3.3 and pH 7.2. Electrophoretic analysis of isolated ciliary axonemes and fractionated oral apparatuses made possible the assignment of polypeptides to structures within the oral apparatus. Approximately 24 polypeptides, including alpha and beta tubulins, are probable components of the basal body-basal plate complex. At least 5 of the oral apparatus polypeptides, including alpha and beta tubulin, are components of the oral apparatus ciliary axonemes. Approximately 138 polypeptides are components of the oral apparatus framework.