ABSTRACT Binding to Trypanosoma brucei of polyvalent IgMs and IgGs, monoclonal IgGs and Fabi fragments of monoclonal IgGs specific for exposed epitopes of T. brucei variant surface glycoproteins (VSGs) was monitored by both immunofluorescence and immu-nocytochemistry. All antibodies and antibody fragments, were uniformly distributed over the parasite surface after incubation with the organism at 0°C. Upon warming to 37 °C bound antibodies and fragments were detected in the flagellar pocket and intracellular organelles. Removal of single layers of bound antibody, or Fabi fragments, from the cell surface at 37 °C, as determined by immunofluorescence, was complete within 20 min and occurred in the presence or absence of protein synthesis. Para-sites that had shown an altered distribution of surface-bound antibody after warming remained fully covered with VSGs of the original antigen type as shown by immunocytochemistry.