Cardiac troponins are important biochemical markers for defining the presence of myocardial injury. However, limitations in troponin testing exist, including the relatively late increase in troponin after onset of ischemia. We therefore evaluated a more sensitive troponin assay for detection of myocardial injury in "early presenters." Discarded serial specimens were obtained from 103 patients who had a negative cardiac troponin I (cTnI) result followed by a positive cTnI result. Results were obtained using our current cTnI method and a new more sensitive assay, TnI-Ultra (Siemens Medical Solutions, Diagnostics Division, Tarrytown, NY). Medical records were reviewed to determine the clinical diagnosis. Precision studies yielded a 10% coefficient of variation at the diagnostic cut points for cTnI (0.10 ng/mL [0.10 microg/L]) and TnI-Ultra (0.04 ng/mL [0.04 microg/L]). TnI-Ultra was positive before cTnI in 66 (64.1%) of 103 cases. We conclude that the more sensitive assay, TnI-Ultra, has better analytic performance and has the potential to detect myocardial injury earlier than the current cTnI assay.