Coelomic fluid of Eisenia foetida earthworms is known to exert strong proteolytic, hemolytic, bacteriostatic, and cytolytic properties. Ultrastructural observations revealed that coelomic fluid causes multiple ruptures and defects in the erythrocyte membrane as well as in the membrane of murine peritoneal leukocytes. Incubation of peritoneal cells in coelomic fluid resulted in a disorganization of the macrophage surface microvilli, changes in the organization of cytoplasmic organelles and disruption and degranulation of mast cells. Severe mesothelial damage was observed after intraperitoneal administration of the coelomic fluid.