Localization and morphology of NO-ergic elements in the digestive system of bivalve molluscs Mactra chinensis and Spisula sachalinensis were studied using histochemical technique  for detection of NADPH-diaphorase (EC 22.214.171.124) . The NO-producing elements were revealed in all parts of the digestive system of the studied animals. NADPH-diaphorase was found in cells of several morphological types as well as in nerve plexuses. The most abundant in the digestive tract parts of the studied molluscs were intraepithelial nerve cells of the “open” type, whose thin apical process is directed towards the gut lumen. Subepithelial NO-ergic neurons were revealed in stomach and crystalline style sac of Mactra chinensis. Besides, diformazan granules are present in brush-border epitheliocytes of the major and secondary ducts of the digestive gland as well as in cells of digestive tubules of this gland. All studied parts were found to contain basiepithelial and subepithelial NO-ergic nerve fibers forming networks of various densities from, most commonly, loose to dense plexuses particularly developed in labia, esophagus, and gut of the studied molluscs.