71 consecutive patients with histologically confirmed sarcoidosis, in various clinical stages of activity, were submitted to 67Ga lung scan, and 23 of them were studied with two or more scans at intervals of 4-6 months. In patients on steroid therapy, the drug was suspended 7 days before scan to avoid the steroids interfering with the gallium (Ga) uptake mechanism. In order to assess the usefulness of 67Ga in the evaluation of sarcoid activity, six other parameters of activity were considered, ranging from angiotensin-converting enzyme levels to progressive symptoms, from deteriorating X-ray or pulmonary function tests to clinical or laboratory evidence of prominent extra thoracic involvement. Our work suggests that Ga scan is more sensitive than chest X-ray in determining the degree and variation of pulmonary sarcoidosis activity, in evaluating the response to therapy, and in foreseeing the relapses. In some cases it gives information not detectable with other noninvasive criteria. The detection of patients with active disease, after discontinuation of steroids 7 days before scan, raises doubts about the opportunities of scanning patients on steroids, and suggests that further studies on this point are needed.