Hematologic study revealed the existence of an anomaly in the leukocytes and platelets of 13 subjects in three generations within a single large family. The platelets were poorly granulated and large (up to 15μ in rare instances). The granulocytes were characterized by a cytoplasmic collection of ribose nucleic acid. The anomaly was transmitted genetically as a simple dominant. The presence of the anomaly was not manifested in any clinically significant symptoms and it was detected only by examination of the blood.