Carbohydrates in thin-sectioned zoospores of the pea root pathogen Aphanomyces euteiches were ultrastructurally localized with the silver methenamine technique. The polysaccharide specificity of localization was verified with minus periodic acid or minus silver methenamine controls, with the sulfhydryl blocker iodoacetate, and with the dialdehyde blockers dimedone and sodium bisulfite. Reaction produce was found on the inner and outer surfaces of the plasma membrane and over the membranes of the water expulsion vacuole system. Inclusions within dense-body vacuoles were covered with reaction product, often in distinct zones. The central core region of K2-bodies, comprising an array of fibers, also contained carbohydrates. Little or no silver methenamine reaction product was found in peripheral vesicles or encystment vesicles, two organelles implicated in cell surface modifications during encystment. This study demonstrates that the cell surface of the unwalled zoospore contains carbohydrates and that the K2-body of A. euteiches, like the K2-body of Saprolegnia ferax, compartmentalizes carbohydrates. We conclude that K2-bodies found in zoospores of two different genera of Oomycetes are homologous organelles. Key words: carbohydrates, zoospore, Aphanomyces, K2-bodies, membranes.