The cytology of samples from broncho-alveolar lavage was studied in 18 patients with stage I or II sarcoidosis, three of whom were smokers (stage II). Cell content was 213 +/- 111.10(3)/ml with 30.8 +/- 15.7 p. cent of lymphocytes for stage I, and 338 +/- 98.10(3)/ml with 34.1 +/- 8.7 p. cent of lymphocytes for stage II patients who were non smokers. In the three patients in stage II who smoked, cell content was 206 +/- 107.10(3)/ml with 15.3 +/- 9.4 p. cent of lymphocytes. Measuring angiotensin conversion enzyme in 12 cases demonstrated elevated (7 cases) or normal (5 cases) levels unrelated to the radiological stage or the lymphocytosis. Diagnosis was confirmed by the presence of characteristic epithelioid granulomas in all cases, in 14 patients after trans-bronchial pulmonary biopsy. In comparison, cell content in 3 cases of extrinsic allergic alveolitis associated with histologically confirmed granulomas was 690 +/- 120.10(3)/ml with 50.3 +/- 10.7 p. cent of lymphocytes, and in 9 cases of different types of intestinal affections was 327 +/- 157.10(3)/ml with 6.33 +/- 7 p. cent of lymphocytes. Constantly elevated lymphocytosis in sarcoidosis constitutes a diagnostic aid; perhaps it can be used during follow-up examinations as a means of assessing progression of the disease. No correlation with the conversion enzyme was noted.