The study of the broncho-alveolar lavage (BAL) has been carried out in 15 consecutive (13 B27) ankylosing spondylarthritis (AS), compared to 17 test subjects. There is no modification of the number of cells, of the percentage of lymphocytes, of the CD4/CD8 ratio, of the beta-2-microglobulin or the conversion enzyme in the BAL liquid between the AS group and the test group. The IgA level of the BAL is lower and the IgA deposits in the bronchial mucosa are more frequent in the AS group (but not in a significant way). Unlike other inflammatory diseases, it seems that there is no subclinical alveolitis in the course of AS.