High blood pressure is a highly prevalent disease, and many patients have uncontrolled blood pressure despite concurrent use of multiple medications (resistant hypertension). This thesis has found increased plasma levels of CCL18, a protein produced from human immune cells, in patients with resistant hypertension. CCL18 is also found to promote the blood vessel damage associated with high blood pressure. Therefore, CCL18 is identified as a potential indicator and treatment target for resistant hypertension.