Bilateral bronchoalveolar lavage (BAL) was carried out in right middle and left upper lobes of 22 nonsmoking females suffering from progressive systemic sclerosis in order to assess interlobar differences and functional correlation of the BAL composition. The patients' age ranged from 20 to 66 years, and the mean disease duration was 10.4 years. The most frequent finding was a mild BAL lymphocytosis (right in 11 of 22 patients; left in 8 of 22), but eosinophilic (right in 11 of 22; left in 5 of 22 patients) and neutrophilic (right in 9 of 22 patients; left in 1 of 22) alveolitis was recognized as well. Differential counts suggestive of alveolitis limited to one of the lavaged lobes were demonstrated in about one fourth of the cases. Including increased cellularity among the criteria of pathological BAL fluid composition, 14% of the subjects showed bilateral BAL results within the normal range. OKT8-positive lymphocytes were significantly increased in 3 patients, but the mean values were not. Total lung capacity, vital capacity, and forced expiratory volume in 1 s correlated inversely with BAL neutrophil (p less than 0.05) and granulocytic (p less than 0.01) differential counts; the strongest, positive correlation was demonstrated regarding the lymphocyte/granulocyte ratios (p less than 0.0005). In conclusion, several patterns of alveolitis as well as a bilaterally normal BAL composition were found in our series; moreover, even if inhomogeneous alveolitis did occur, a single lavage performed in the right middle lobe correctly detected or excluded the presence of an alveolitis in 95% of our patients.