Of various hereditary abnormalities of WBC morphology, the most important is the Pelger-Huлt nuclear anomaly. This is manifested by WBC nuclear hyposegmentation. In the neutrophil series, many of the segmented cells appear to have bilobed nuclei shaped like a dumbbell or a pair of eyeglasses. There is also an increase in bandlike forms and forms with round or oval nuclei resembling myelocytes. Eosinophils normally may have a bilobed nuclear form. Although occasional normal neutrophils may have this nuclear shape, it is not a common finding, and more than two or three neutrophils with a bilobed nucleus per 100 WBCs would be unusual. The Pelger-Huлt anomaly may be congenital, inherited as a mendelian dominant trait; the congenital form is not common and is asymptomatic. An increased number of neutrophils with similar appearance may represent an acquired change (known as pseudo-Pelger-Hu?t); this is most often seen in myeloproliferative disorders, myeloid leukemia, and agranulocytosis, in some patients with metastatic tumor to bone marrow, or under conditions of drug toxicity. Neutrophils of the Pelger-Hu?t anomaly must be differentiated from true neutrophil immaturity such as that seen with infection or chronic myelogenous leukemia.