The value of different factors are examined to assess activity in 60 patients with biopsy-proven sarcoidosis. In patients with active sarcoidosis (n = 35), 67Gallium scans proved to be the most sensitive method (94 percent sensitivity), followed by serum angiotensin I converting enzyme (S-ACE) levels, chest x-ray films, and lymphocyte assays. In patients with peripheral pulmonary lesions, chest x-ray films failed in 32 percent of cases to document activity (68 percent sensitivity) whereas 67Ga scans and S-ACE levels remained to give reliable results. Despite poor specificity, negative 67Ga scans together with normal ACE levels have a high predictive value for exclusion of active sarcoidosis. In patients with peripheral pulmonary lesions, chest roentgenography is of doubtful value for staging lung involvement and assessment of activity including monitoring and control of therapy.