The phytohemagglutinin, concanavalin A (Con A), interacts specifically and reversibly with the polyglucosyl glycerol phosphate teichoic acid of Bacillus subtilis 168 cell walls. Advantage has been taken of this interaction to examine the organization of the surface teichoic acid at the ultrastructural level. Con A-treated whole cells and cell walls contain an irregular, fluffy layer 25 to 60 nm thick which is absent in untreated or alpha-methyl glucoside-treated preparations. This discontinuous layer is present only on the outer profile of Con-A-treated cell walls. The surface teichoic acid is proposed to be oriented perpendicular to the long axis of the cell. Fixation and embedment for electron microscopy result in condensation of this layer which then contributes to the stainable portion of the wall. Con A treatment binds adjacent teichoic acid molecules in their native configuration producing the irregular, fluffy layer visualized.