While the knowledge concerning the role of the immune system in many internal disorders has grown rapidly in recent years, there are few methods to assess immune system activation in clinical practice. Measurement of urine neopterin, product of a metabolic pathway controlled by interferon-gamma, has been found useful in many clinical conditions. The present study concerns neopterin excretion in 157 patients with different internal disorders. As expected, we found an increase in urine neopterin in patients with malignant tumors, autoimmune disorders like systemic lupus erythematosus or inflammatory bowel disease, and infections. Elevated neopterin levels were also observed in acute pancreatitis and in acute myocardial infarction. In addition, significant correlations between urine neopterin and zinc and neopterin and copper excretion were found suggesting a physiological role of neopterin as urine antioxidant.