Idiopathic pulmonary fibrosis (IPF) is characterized by progressive, irreversible scarring of the lung parenchyma that can require invasive diagnostic testing (1). Interstitial lung abnormalities (ILAs) have been described in the general population (2). Among asymptomatic first-degree relatives of patients with familial interstitial pneumonia (FIP), 14% have radiologic ILAs and 35% have interstitial abnormalities on biopsy (3). In the Framingham population, fibrotic ILAs were present in 1.8% of subjects> 50 years of age (4) and associated with increased risk of death (5, 6), suggesting ILAs may be a harbinger of IPF. Because ILAs include ground glass and diffuse centrilobular nodularity can be present without fibrosis of the lung, we created the term “preclinical pulmonary fibrosis”(PrePF)(7) to identify firstdegree relatives of patients with FIP (a high-risk cohort) not known to have interstitial lung disease who have features of lung fibrosis on high-resolution computed tomography. We used proteomic analyses of plasma to identify circulating markers of IPF and then determine if IPF-associated proteins are predictive of PrePF. Some of the results of these studies have been previously reported in the form of an abstract (8).