Leikotsity (L) - belye kroviannye kletki (6-8 tonn v 1 mkl), imeyushchie yadra. Oni podrazdelyayutsya na granulotsity (neytrofily, bazofily, eyozinofily) i agranulotsity (limfotsity, monocity). V techeniye sutok i sezonov goda kolichestvo leikotsitov menyaetsya, ne postoyanno. Uvelicheniye leikotsitov - leikotsitoz (fiziologicheskoe, patologicheskoe), umen'sheniye - leikopeniya (luchevaya bolezn'). Leikotsity v organizme vypolnyayut zaschitnuyu rol' (immunitet), protivostoyat mikrobam, virusam, prosteishim, chuzherodnym veschestvam.