Infective larvae of the parasite nematode Toxocara canis were incubated in vitro with murine eosinophils, neutrophils and non-induced and induced macrophages. The interactions between the different types of cells and the worms were observed in the presence or absence of immune mouse serum and/or complement. Cells showed considerable differences in the manner, duration and outcome of this interaction. Despite the adhesion of cells to the larvae of T. canis, there was no evidence of damage to the worms. Scanning and transmission electron microscopic observations suggest that the cells adhere to the cuticular surface via an electron-dense material. This material might play a protective role against the helmintotoxic capacity of the inflammatory cells.