The localization and distribution patterns of non-specific esterases (NSE) and acetylcholinesterase (AChE) activities in adult female Onchocerca fasciata (Filarioidea: Onchocercidae) have been determined using enzyme histochemical techniques. NSE activity was highest in the hypodermis and mild to moderate in the somatic musculature and uterine epithelium. The intensity of the reaction was decreased but not eliminated by sodium fluoride. AChE activity was found in the hypodermis and cuticle of the female worm, highest in fully formed microfilariae in the uterus, whereas early oocytes and embryonic forms were negative. Butyrylcholinesterase activity showed similar but less intense staining reactions at the same sites. Eserine-treated sections showed no AChE activity in all areas where it is usually present. The present techniques failed to demonstrate AChE activity in the nervous tissue including the hypodermal nerve trunks and neuromuscular junctions of the worm. The possible functional significance of the demonstrable enzymes was discussed with respect to their location. NSE activity may be involved in lipid metabolism, whereas AChE activity may have a role in host-parasite relationship.