To determine if examination of respiratory secretions is useful in diagnosing Pneumocystis carinii pneumonia, smear preparations of expectorated sputum, tracheal aspirates, and transtracheal aspirates stained by the Gomori methenamine silver nitrate method were examined. Pneumocysts were observed more frequently in material obtained by transtracheal aspiration than in secretions obtained by the other methods. Transtracheal aspiration yielded material containing pneumocysts in 8 (13%) of 60 patients; each had pulmonary infiltrates and clinical courses consistent with P carinii pneumonia. Of 330 smear preparations examined from expectorated sputum, three patients had pneumocysts in their sputum and one had organisms in both transtracheal aspiration and expectorated sputum; all three had pneumonia. This study provides evidence that transtracheal aspiration is a useful initial step in the approach to the diagnosis of P carinii pneumonia.