Infiltrative diffuse lung diseases represent a heterogenous group of lesions with overlapping clinical and roentgenological features. Their diagnosis frequently needs a pathologic approach. We report our experience (671 patients with lung infiltrates) with transbronchial lung biopsy (TBB) procedure. The results of morphologic investigation were subdivided into three groups: 1) A specific morphologic diagnosis was made in 192 cases (29%) 2) Histopathologic changes well consistent with the clinical pattern were present in 258 patients (38%) 3) Non-specific lesions were found in 221 cases (33%). The diagnosis yield of the method was of 67%. UIP, DIP, Pulmonary Angiitis and Granulomatosis, Bronchiolitis Obliterans-Organizing Pneumonia and other rarer lung diseases may not be diagnosed on the basis of lesions present in TBB specimens.