There are many different types of leukemia, but all are a malignant disease of the white blood cells of the body. The cause of all types is still uncertain. Each type is determined by the specific blood cell involved and the length of time the illness lasts. Leukemia exists in both an acute ad chronic form: it is detected when the blood is examined. When the cell group known as the lymphocytes is affected, the disease is called lymphocytic leukemia. When the monocytes are involved, it is known as monocytic leukemia. And when the polymorphonuclear cells are involved, it is called myeloid leukemia.