Do you know about bone marrow, one of the major blood-forming organs in the body? What is bone marrow extraction and bone marrow transplantation all about? Is it scary? Here we will briefly describe the routine bone marrow aspiration tests in hematology clinics, so that you can understand the basic situation. Human hematopoiesis goes through different stages from prenatal yolk sac hematopoiesis, hepatopoiesis (including spleen, kidney, thymus, lymph nodes, etc.), and bone marrow hematopoiesis, to postnatal hematopoiesis of bone marrow gradually increasing and hepatosplenic hematopoiesis gradually decreasing, and finally bone marrow becomes the main hematopoietic organ of human body and maintains lifelong hematopoietic function. Therefore, bone marrow is the most important organ for the production of our blood cells (red blood cells, white blood cells, platelets, etc.) and the largest organ in the human body. It consists of nerves, blood vessels, stromal cells, etc., and is filled with various hematopoietic cells in between. Therefore, when blood count indicates an abnormal increase or decrease in blood cells, we should further examine the bone marrow, which is the source of blood cell production, to understand how the bone marrow is producing blood and to assist in the diagnosis. Bone marrow aspiration is a procedure in which a bone marrow needle is inserted into the bone marrow cavity with the help of local anesthetic medication and a small amount of bone marrow blood is extracted for examination. Bone marrow examination is one of the basic tests for hematopoietic disorders and is the main tool for assessing the prognosis and efficacy of treatment for many hematologic disorders. The main sites for bone marrow aspiration are the posterior superior iliac spine, the anterior superior iliac spine and, if necessary, the sternal stalk. Generally, only 0.5 ml of bone marrow blood is required for bone marrow aspiration (if necessary, 8 ml of bone marrow blood is retained for further systematic examination), and the adverse effects are mainly a little pain during the puncture and extraction of bone marrow blood, but there is no obvious damage to the human body, and there are no fearful adverse effects such as back pain or paralysis. In addition, since the bone marrow is a blood-forming organ, theoretically, the recovery time after bone marrow blood extraction should be faster than that after blood sampling. Therefore, there is no need to be overly concerned or unnecessarily resistant to bone marrow aspiration. Bone marrow transplantation is an effective treatment for many hematological malignancies including leukemia, lymphoma, myeloma, bone marrow hematopoietic diseases including aplastic anemia, other severe autoimmune diseases and solid tumors. In the past, it was called bone marrow transplantation because of the use of bone marrow stem cells from a healthy donor, and has been used ever since. In fact, bone marrow transplantation is also known as hematopoietic stem cell transplantation, which is a treatment that uses hematopoietic stem cells to replace the patient’s diseased bone marrow/stem cells, so that normal bone marrow/stem cells can differentiate and proliferate normally, thus restoring health. Since stem cells have the function of self-renewal and proliferation, there is no substantial damage to healthy bone marrow/stem cell donors, who can just take rest after donating bone marrow/stem cells. Let’s all lend a helping hand and let love hold up a rainbow.