No EPO was added in any of the experiments, but the CML cells consistently produced erythroid colonies without EPO, often including large or X-large BFU-E, and sometimes comprising over half of the total colonies, whereas in the absence of EPO, the normal cells rarely produced any erythroid colonies and then only tiny or very small ones. This evidence concerns the gene EPO and chronic myelogenous leukemia, BCR-ABL1 positive.