A remarkable increase in the number of recognized clinical abnormalities of neutrophil function has occurred within the 8 years past. Of major importance in the delineation of these disorders is the establishment of appropriate methodology of their characterization. This review discusses phagocytosis and its disorders by dividing it into stages that encompass the way in which phagocytes ferret out injection, how they recognize pathogens and the intracellular events leading to engulfment and killing of micro-organisms. The pathology of chemotaxis and random mobility is described: the lazy leukocyte syndrome, the Chediak-Higashi syndrome, the familial chemotaxis pecular dermatosis, and a variety of serum abnormalities of the serum complement system associated with deficient generation of chemotactic activity. The second part of these disorders is dailing with the inherited abnormalities of the oxygen dependent killing mechanisms of phagocytes, the chronic granulomatous disease, the glucose-6-phosphate deshydrogenase deficiency, the myeloperoxydase deficiency and the glutathione peroxydase deficiency.