To determine the effectiveness and accuracy of transbronchial fine needle aspiration of mediastinal masses for the staging of bronchogenic carcinoma, the results and histologic correlations of 97 transbronchial aspirates submitted from 78 patients over a two-year period were reviewed. Malignant cells were present in 25 of 97 aspirates. Of the remaining 75 nonmalignant aspirates, 34 had corresponding mediastinal tissue sections. Review of these 34 aspirates disclosed respiratory epithelial cells without lymphocytes in 20, lymphocytes without respiratory cells in 1 and both cell types in 8. Neither cell type was present in five aspirates. The predictive value of a negative result was 78% for nonmalignant aspirates containing lymphocytes and 36% for nonmalignant aspirates not containing lymphocytes (P less than .05). The presence of lymphocytes in transbronchial needle aspirates of the mediastinum is an essential criterion of specimen adequacy. Negative specimens lacking lymphocytes should be considered unsatisfactory, regardless of the numbers of respiratory epithelial cells present.