Nongranulomatous, nonspecific interstitial pneumonitis was a predominating or prominent histopathologic finding in 62 percent of 128 granuloma-containing specimens from open lung biopsies obtained from patients with sarcoidosis. Data from this study, combined with observations by others on the evolution of experimentally induced granulomas, indicate that interstitial pneumonitis represents a very early lesion, possibly the initial lesion, in pulmonary sarcoidosis. Because of the relatively large error of sampling inherent in the currently increasing practice of obtaining small specimens for lung biopsy via the flexible fiberoptic bronchoscope, we anticipate that interstitial pneumonitis will be seen as the only histopathologic finding in these specimens with increasing frequency. It is therefore important to recognize that interstitial pneumonitis is a characteristic, although nondiagnostic, morphologic feature of pulmonary sarcoidosis.