Scanning and transmission electron microscopy of Trypanosoma congolense epimastigotes attached to a plastic substratum shows them to elaborate a complex flagellum filament system and plaque with a highly organized structure. Non-ionic detergent extraction of these cells shows that the resulting cytoskeletons remain attached to the plaque. The subpellicular corset of microtubules can be removed by salt or Ca+2 treatment leaving the axoneme, paraflagellar rod, associated filaments and the plaque. Neither of these treatments therefore removed the plaque-associated material from the substratum. Analysis of these fractions by SDS–polyacrylamide gel electrophoresis reveals an abundant 70 kDa protein that is highly enriched in the salt extracted ‘minimal plaque’ structures and appears likely to be a major constituent of this structure. These studies reveal that the complex filament and microtubule systems of the cytoskeleton involved the attachment of trypanosomes to substrata and have established a method of biochemical fractionation of the structures and components involved.