In 60 patients with histologically proven sarcoidosis, 67Ga scanning was evaluated in terms of sensitivity and specificity for assessing disease activity and compared with chest radiography, serum ACE and blood T-lymphocytes. While 67Ga scans had the highest sensitivity (94%), the specificity was only 68%. The sensitivity of chest radiography was 80%, of serum ACE and blood T-lymphocytes 77% and 48%, respectively. While in patients with radiographical type I, 67Ga scanning, chest radiography and serum ACE had a sensitivity of 92%-100%, in patients with radiographical type II-III, only 67Ga scans had a sensitivity exceeding 90%. A 67Ga score correlated significantly with serum ACE levels (r = 0.59, P less than 0.001). After effective steroid treatment, 67Ga uptake and serum ACE activities decreased markedly. While in 25% of cases, chest radiography failed to provide reliable information, 67Ga scanning and serum ACE activities always proved useful in evaluating the course of the disease and the patient's response to steroid therapy. A negative 67Ga scan together with normal serum ACE levels seem to have a high predictive value for excluding active sarcoidosis.