The cell envelope of Wolinella recta was studied by electron microscopy. In thin sections the surface layer (S-layer) seemed to be in close contact to the outer membrane (OM). A hexagonally arranged pattern of the S-layer was revealed by freeze-etching. Unlike in other oral bacteria with an S-layer, the cleavage occurred along the S-layer by freeze-fracture, suggesting an exceptionally tight relationship between the two outermost layers. The convex surface of the S-layer was usually revealed by this technique. When cleavage occurred through the outer membrane, no periodicity was seen in the arrangement of the intramembranous particles.