Bronchoalveolar lavage fluid of patients with four interstitial lung diseases (sarcoidosis, idiopathic pulmonary fibrosis, pulmonary Langerhans cell histiocytosis, fibrosis associated to systemic sclerosis) and smoker and non smoker control subjects were compared in a proteomic study. Principal Component Analysis was used to statistically verify the association between differentially expressed proteins and the conditions analyzed. Pathway and functional analysis by MetaCore and DAVID software revealed possible regulatory factors involved in specific “process networks” like regulation of stress and inflammatory responses. Immune response by alternative complement pathways, protein folding, Slit-Robo signalling and blood coagulation were “pathway maps” possibly associated with interstitial lung diseases pathogenesis. Four interesting proteins plastin 2, annexin A3, 14-3-3ε and S10A6 (calcyclin) were validated by western blot analysis. In conclusion, we identified proteins that could be directly or indirectly linked to the pathophysiology of the different interstitial lung diseases.