General cytological and ultrastructural features of cells found in the peripheral blood of three captive beluga whales (Delphinapterus leucas) are described. We noted all major peripheral cell types common to the circulation of mammalian species, including polymorphonuclear neutrophils, eosinophils, basophils, lymphocytes, and monocytes, as well as myelocytes, erythroblasts, and plasma cells. Platelets and two populations (normal and hypochromic) of red blood corpuscles were observed.