Detection of autoantibodies in human serum assists in the diagnosis of patients with autoimmune diseases. Diagnostic antibody signatures have also been proposed for colon, pancreatic, and breast cancers. In this issue of the JCI, Cleutjens et al. describe the application of a peptide array technique toward the development of antibody biomarkers of ruptured atherosclerotic lesions (see the related article beginning on page 2979). A phage-display library was prepared from mRNA derived from ruptured peripheral human atherosclerotic plaques, and the phages containing immunoreactive peptides were screened with serum from patients with ruptured atherosclerotic lesions. Antibodies reacting with 2 peptides, E1 and E12, were particularly sensitive for the early diagnosis of acute myocardial infarction. Further studies that include an adequate number of patients presenting very early after the onset of symptoms and additional control patient populations are warranted to compare the utility of these biomarkers to those in clinical use.