Bronchoalveolar lavage was performed in 14 patients suffering from histologically confirmed Wegener's granulomatosis who also showed x-ray signs of lung involvement. Cell distribution and immunophenotypical characterisation of lymphocytes and alveolar macrophages of patients suffering from Wegener's granulomatosis were compared with the findings obtained from 10 controls. The bronchoalveolar lavage of the granulomatosis patients showed a significant increase of the total cell count, signalling inflammatory involvement of the lung. Differential cytgological analysis showed a significant increase in the total number of granulocytes in the lavage fluid of the Wegener's granulomatosis patients (in one case up to 40%). The median granulocyte count was increased fivefold compared with the control. The increase of the granulocyte count was mainly conditioned by an increase in the number of neutrophilic granulocytes but there was also a significant increase in eosinophilic granulocytes. There was also a slight but significant increase in the lymphocyte count in the bronchoalveolar lavage fluid of patients with Wegener's granulomatosis. The number of CD-3-positive lymphocytes was significantly higher than with the controls. No significant differences were noted for the CD-4-positive, CD-8-positive and CD-19-positive lymphocytes. Immunophenotyping of the alveolar macrophages with monoclonal differentiation markers of the Ki-M-Series showed that the alveolar macrophages of patients with Wegener's granulomatosis resembled an immunophenotype that was close to that of monocytes. The number of proliferating macrophages was also higher than with the controls.