ABSTRACTThe cultured somatic (assimilative) stage ofEndogone pisiformis(Endogonales) was examined ul- trastructurally and cytochemically. The fungus produces thin-walled, coenocytic and irregularly shaped hyphae with many swellings. The cell wall is thick and is organized into two layers, an outer electron-lucent layer and an inner electron-opaque layer. The cytoplasm of the hyphae and swellings shows considerable morphological variation based on the sampling site in the colony. Young cells sampled at the margin of the colony have granular protoplast rich in cellular organelles and membrane profiles, while those sampled 1–2 cm away from the margin of the colony are vacuolated with abundant lipid and glycogen inclusions. Intrahyphal hyphae are frequently observed in mature hyphae and hyphal swellings ofE. pisiformis.Specific macromolecules were identified and localized in different cellular organelles ofE. pisiformisby using different enzyme- and lectin-gold complexes,α-amylase-gold and phospholipase-gold complexes labeled glycogen inclusions and phospholipids respectively. Sugar residues, such as N-acetylglucosamine, fucose and mannose, were localized in different organelles, using wheat germ agglutinin,Ulex europaeusand Concanavalin A lectins respectively. The cytochemical results are discussed in relation to the development ofE. pisiformis, along with speculations on the function and significance of these macromolecules.