Basophils are the least common type of leukocyte.

The statement is true. Basophils are indeed the least common type of leukocyte in the peripheral blood, typically comprising only 0 to 1 percent of the total white blood cell count. This makes them the rarest of all the granulocytes and the rarest leukocyte overall. By comparison, neutrophils are the most abundant, making up approximately 50 to 70 percent of circulating leukocytes, followed by lymphocytes at roughly 20 to 40 percent, monocytes at 2 to 8 percent, and eosinophils at 1 to 4 percent. Basophils are easily identified under the microscope by their large, coarse, dark purple-to-black granules that often obscure the bilobed nucleus. Functionally, basophils are closely related to mast cells found in tissues and play important roles in allergic responses and hypersensitivity reactions by releasing histamine, heparin, and other vasoactive mediators. Despite their low numbers in circulation, they become clinically significant in conditions such as allergic asthma, anaphylaxis, and, notably, in certain hematological malignancies where basophilia can be a hallmark finding, as seen in chronic myelogenous leukemia.