Serum and urinary neopterin levels were determined by high pressure liquid chromatography in 26 patients with pulmonary sarcoidosis and 12 healthy controls. Neopterin levels were significantly higher in sarcoidosis patients than in the controls. Neopterin levels differed from serum angiotensin converting enzyme (ACE) activities and were significantly higher in radiologic stage 1 and 2 than in radiologic stage 0 in patients not receiving prednisolone. No significant correlation was found between neopterin level and serum ACE activity. On the other hand, a significant correlation was found between neopterin level and serum adenosine deaminase activity. We believe that serum and urinary neopterin levels may be a more clinically valuable method of assessing pulmonary sarcoidosis than serum ACE activity.