Many oncology practices treat patients with benign and malignant hematologic diagnoses. As a result, oncology nurses often are required to care for these patients. One common procedure nurses perform is therapeutic phlebotomy, where about 500 ml of blood is removed through a large-bore needle over 15-30 minutes. The procedure is ordered as a treatment for hereditary hemochromatosis, polycythemia vera, and secondary polycythemia. Before initiating the procedure, nurses must be aware of a patient's diagnosis, baseline hemoglobin, hematocrit, ferritin, and therapeutic end points. Reviewing these diagnoses will help nurses understand why phlebotomy is an important part of treatment.