We performed a cytogenetic analysis of eosinophilic colonies grown from bone marrow culture of a patient with acute myelogenous leukemia (FAB-M2) associated with t(8;21). The bone marrow, in which 50.2% myeloblasts and 5.6% eosinophils were observed, gave rise to eosinophilic colonies, as well as colonies consisting of immature myeloid cells. The cytogenetic analyses of the colonies were performed on two occasions. The first study revealed t(8;21) in 15 of 16 metaphases in randomly plucked colonies from a dish, in which 65% of the total colonies were those consisting of immature myeloid cells and 35% were eosinophilic colonies identified by positive staining with Luxol-Fast-Blue. The second study, in which eosinophilic colonies were selectively plucked for cytogenetic analysis, showed Cq- and Gq+ markers, which were considered to be t(8;21), in all metaphases (6/6). Our present study strongly suggests that an involvement of the eosinophilic series in the leukemic process of this patient.