Surface-labelling techniques have been used to delineate a number of constituent molecules of the cuticle in adult stage Brugia malayi and Brugia pahangi. These molecules can be separated by virtue of their physical properties, and localised either by sequential solubilisation of intact cuticles or immunoelectron microscopy with relevant antisera. The major structural components of the cuticular matrix consist of a set of collagenous proteins of diverse molecular weight ranging from 36 to 160 kDa, cross-linked by disulphide bonds and confined to the basal and inner cortical layers. Each stage of the parasite has a distinctive set of between 12 to 25 collagenous proteins whose synthesis is regulated temporally with respect to moulting. As in other nematodes, the outer cortex and epicuticle is composed of a cross-linked insoluble proteinaceous structure. Two non-structural and water-soluble proteins are also resolved by Iodogen-mediated labelling; a 15 kDa peptide which shows no evidence of glycosylation, and a major 29 kDa glycoprotein, which carries at least two N-linked oligosaccharide chains and which we have termed Gp29. The former protein can be detected in L3, L4 and adult B. malayi by surface labelling, whereas Gp29 appears to be restricted to L4 and adult worms. The possible significance of cuticular proteins as targets of immunity or causative agents of pathology is discussed.