The role of tumour necrosis factor-alpha (TNF-α) in the development of autoimmune pulmonary inflammation has been investigated in lupus-prone mice. An increase in TNF-α mRNA level from whole lung preparation of lupus-prone mice was evident, from 3 weeks to 12 weeks during growing process, as shown by Northern blot analysis, but not in control mice. Furthermore, it is also found that the major source of this increase in TNF-α mRNA was attributed to infiltrating mononuclear cells found within the lung. Treatment of lupus-prone mice with rabbit anti-mouse TNF-α IgG prevented the development of pulmonary inflammation lesions such as lung fibrosis and alveolitis. These results suggest that an increased TNF-α production by infiltrating mononuclear cells in the lungs of lupus-prone mice may play a role in the development of autoimmune pulmonary inflammation and in significant changes of cytokines and the immune responses in pulmonary inflammation lesions of lupus-prone mice.