ABSTRACTThe subcellular location of carbohydrates in secondary zoospores ofSaprolegnia feraxwas determined from an electron cytochemical study. Specificity of reactions was verified with the sulfhydryl blocker iodoacetate, and the dialdehyde blocker dimedone. Although no cell coat was visible on the zoospore surface, the plasma membrane and the flagellar sheath contained an abundance of carbohydrate and sulfhydryl compounds. Deposition of reaction product and results of controls demonstrated that similar compounds were also on membranes of the water expulsion vacuole system. Peripheral vesicles contained reaction product over their fibrous contents, demonstrating the presence of carbohydrates, and controls indicated that sulfhydryl groups were most likely also present. Sulfhydryl-containing carbohydrates and other carbohydrates were compartmentalized in the tubule-filled cavity of kinetosome-associated organelles (K2bodies), while their granular matrix was unreactive. Vital roles of carbohydrates in oomycetous zoospores are incompletely understood, but this study suggests mechanisms through which they may function in the stability and recognition of membranes. This is the first report of carbohydrates in K2bodies and provides a basis to explore the function of this novel organelle.