Idiopathic pulmonary fibrosis is a fatal disorder characterized by interstitial fibrosis and parenchymal inflammation. Current concepts of this disease suggest that the inflammation precedes and probably induces the fibrotic state. To evaluate the extent and relative activity of the inflammatory process, we scanned patients with idiopathic pulmonary fibrosis using gallium-67, a radionuclide known to concentrate in regions of inflammation. To quantify the amount of isotope in the lung parenchyma, the 67Ga-index was developed, a parameter derived from estimates of the size of regional pulmonary uptake, the uptake intensity, and its texture. Evaluation of 67Ga scans in 30 patients with idiopathic pulmonary fibrosis and 19 control subjects demonstrated that the 67Ga-index in the group with idiopathic pulmonary fibrosis was significantly higher (P less than 0.001) than that in the control group. When compared with lung biopsy morphologic studies in 22 patients with idiopathic pulmonary fibrosis, the 67Ga-index correlated with the degree of interstitial cellularity (P less than 0.05) and the degree of alveolar cellularity (P less than 0.005). When compared with cellular analysis of bronchoalveolar lavage fluid in 17 patients with idiopathic pulmonary fibrosis, the 67Ga-index correlated with the differential percentage of neutrophils (P less than 0.05), but not lymphocytes, eosinophils, or macrophages. These studies indicate that 67Ga accumulates in the lungs of patients with idiopathic pulmonary fibrosis and is probably associated with the active inflammatory state. The associations of the 67Ga-index with morphologic features and bronchoalveolar lavage analysis suggest that quantitative evaluation of these scans may be useful in staging the activity of idiopathic pulmonary fibrosis and following responses to therapy.