Several experimental findings suggest an association between interstitial lung diseases and autoantibodies. Antibodies against lung tissue including pneumocytes type II in patients suffering from idiopathic pulmonary fibrosis (IPF) were reported in recent years. In this investigation the serum of 103 persons (10 with IPF, 23 with M. Boeck, 18 with rheumatoid arthritis (RA) and 52 healthy controls) was examined for autoantibodies against pneumocytes type II and Clara cells by indirect immunofluorescence on human lung tissue. These antibodies against both cell types are an additional proof for common antigens in pneumocytes type II and Clara cells. The autoantibodies were present in similar frequency in the 4 groups (IPF: 20%, M. Boeck: 26.1%, RA: 22.2% and 23.1% of the healthy controls). So no significant association was found between the antibodies and the interstitial lung diseases. A role of the antibodies in the pathogenesis of the diseases, however, can not be excluded by this study. A possible role as parameter of development of interstitial lung diseases should be subject to further investigations in form of a prospective follow up study.