Interstitial lung diseases (ILDs) are a heterogeneous group of multiple pulmonary disorders. ILDs are characterized by an irreversible architectural distortion and impaired gas exchange; however, there is great variability in the clinical course. ILD diagnosis requires a combination of clinical data, radiological imaging and histological findings. It is necessary to find reliable predictors for the disease progression. Peripheral blood biomarkers offer the advantages of being readily obtained, non-invasive, and serially monitored. At the same time, successful management of ILD patients strictly depends on an accurate and confident diagnosis. In this context, the detection of reliable biomarkers able to identify ILD subtypes. This review focuses on selected validated and/or potentially interesting biomarkers investigated in the peripheral blood and lung tissue of patients with ILD associated with Connective tissue disease (CTD)