The body walls of infective 3rd-stage larvae of S. venezuelensis were studied by routine transmission electron microscopy, ruthenium red cytochemistry, quick-freeze, freeze-fracture and deep-etch techniques. In routine thin sections the cuticle is formed by 5 layers: epicuticle, cortical, medial, fibrous and basal. The epicuticle showed a trilaminate appearance and a surface coat stained with ruthenium red. Specimens submitted to freeze-fracture were frequently sectioned along the body wall at the level of the hypodermis, showing the E and P fracture faces of the outer and inner hypodermal membranes. In replicas of fractures submitted to etching, the external surface of the nematode was exposed, revealing particles and fine strands of fibrous elements, and was sometimes covered by a well organized structure with a crystalline pattern. At the level of the cortical, medial and basal layers, interconnecting fibrous and globous structures were seen. The fibrous layer was formed by parallel bars of thick fibrous elements. The cytoskeleton of the hypodermis and muscle cells also became evident with this technique.