ABSTRACT. Cartwheel complexes reassembled in a fraction derived by treating isolated oral apparatuses from Tetrahymena with 1.0 M KC1 for 12 h. Approximately 40% of the KCl‐soluble protein reassembled into cartwheel complexes. The reassembly reaction was protein‐concentration dependent, and reassembled cartwheels were stable at 3° C. Sucrose gradient centrifugation resolved 3 high molecular mass protein complexes from the KCl‐soluble fraction. Each of the 3 complexes has a different mass, but each contains the same 5 polypeptides, 2 of which arc probably tubulins. When these complexes were removed from the KCl‐soluble fraction by high speed centrifugation, cartwheel reassembly did not occur. The 5 polypeptides in the high molecular mass complexes were among several other polypeptides resolved from reassembled cartwheels by 2‐dimensional gel electrophoresis. The high molecular mass complexes are probably essential for cartwheel formation. The electrophorctic data also show that several polypeptides in the KCL‐soluble fraction do not appear to be incorporated into cartwheels. These polypeptides are probably non‐essential for cartwheel formation.