The epicuticle of adult Moniliformis dubius is resolved as a filamentous coat external to the superficial limits of the tegument trilaminate unit membrane but intimately associated with its structure. Light and electron microscope level histochemical procedures for the demonstration of acidic polyanions suggest the association of mucopolysaccharides with the composition of this hirsute surface investment. The presence of neutral polysaccharides and/or glycoproteins is also indicated by the staining of the epicuticle by the periodic acid-Schiff and periodate-silver methenamine reactions. Thus, the acanthocephalan epicuticle is cytochemically and morphologically reminiscent of the polyelectrolytic glycocalyces described for many vertebrate and invertebrate cell types. These observations are discussed in reference to the biological activities of the acanthocephalan body surface.