This book examines the latest research developments in the field of basophil granulocytes, sometimes referred to as basophils, which are the least common of the granulocytes, representing about 0.01% to 0.3% of circulating white blood cells. The name comes from the fact that these leucocytes are basophilic, i.e., they are susceptible to staining by base dyes, as shown in the picture. Basophils contain large cytoplasmic granules which obscure the cell nucleus under the microscope. However, when unstained, the nucleus is visible and it usually has 2 lobes. The mast cell, a cell in tissues, has many similar characteristics.