SYNOPSIS.An extracellular surface coat was observed at the fine‐structural level on the outer lamina of the pellicular and flagellar membranes of intactTrypanosoma musculibloodstream forms. The surface coat had a mean width of 9.2 nm, and was composed of a somewhat electron dense, uneven, fibrillar‐like matrix. Brief trypsin treatment of living blood forms completely removed the cell surface coat.Several cytochemical methods applicable to electron microscopy were used to detect the presence and distribution of carbohydrates in the trypanosome's surface coat and pellicular membrane. The polycationic dye compounds employed were: ruthenium red, ruthenium violet, Alcian blue chloride, and lanthanum nitrate. Electron‐dense stain reaction products, indicative of polysaccharides, were evident in the surface coat of cells treated with these dyes, which also agglutinated both living and glutaraldehyde fixed cells. Like the surface coat, the pellicular membrane of trypsinized cells gave strong positive staining reactions with the several dyes, indicating the presence of membrane bounded carbohydrates, and living and glutaraldehyde‐fixed trypsinized cells were agglutinated with the polycationic stains. Bloodstream forms were treated with the enzymes, α‐amylase, dextranase, and neuraminidase. No obvious morphologic difference, however, was apparent between the surface coat of untreated cells and those subjected to treatment with any of the various glycoside hydrolase enzymes. Further, these enzymes had no apparent gross effect on the staining affinity of the surface coat for the several polycationic dyes. Cationized ferritin was used to visualize the negative cell surface charge ofT. musculibloodstream forms. Large quantities of cationized ferritin were bound in the surface coat matrix. Glycoside hydrolase enzyme treatments had no apparent effect on the amount of ferritin bound in the surface coat. Cationized ferritin was bound also to the outer lamina of the pellicular membrane in trypsinized cells, which had quantitatively less ferritin bound per surface unit area than bloodstream forms untreated by the enzyme. Living and glutaraldehyde‐fixed cells were agglutinated with cationized ferritin. The results obtained in the various experiments indicated that polyanionic polysaccharides were constituent terminal ligands of the surface coat matrix and pellicular membrane inT. musculiblood