Macropinocytosis is a form of endocytosis that accompanies cell surface ruffling. It is distinct in many ways from the better characterized micropinocytosis, which includes clathrin-coated vesicle endocytosis and small uncoated vesicles. Because macropinosomes are relatively large, they provide an efficient route for non-selective endocytosis of solute macromolecules. This route may facilitate MHC-class-II-restricted antigen presentation by dendritic cells. Because the ruffling that leads to macropinocytosis is regulated, it has been exploited by some pathogenic bacteria as a novel route for entry into cells.