Troponin I is a specific and sensitive clinical biomarker for myocardial injury. In this Study we have used polyvalent phage display to isolate unique linear peptide motifs which recognize both the human and rat homologs of troponin I. The peptide specific for human troponin I has a sequence of FYSHSFHENWPS and the peptide specific for the rat troponin I has a sequence of FHSSWPVNGSTI. Enzyme-linked immunosorbent assays (ELISAs) were used to evaluate the binding interactions, and the two phage-displayed peptides exhibited some cross-reactivity, but they were both more specific for the troponin I homolog they were selected against. The binding affinities of the phage-displayed peptides were decreased by the presence of complex tissue culture media (MEM), and the addition of 10% calf serum further interfered with the binding of the target proteins. Kinetic indirect phage ELISAs revealed that both troponin I binding peptides were found to have nanomolar affinities for the troponin proteins while attached to the phage particles. To our knowledge, this is the first example of isolation and characterization of troponin I binders using phage display technology. These new peptides may have potential utility in the development of new clinical assays for cardiac injury as well as in monitoring of cardiac cells grown in culture. Biotechnol. Bioeng. 2010;105: 678-686. (C) 2009 Wiley Periodicals, Inc.