We have evaluated the analytical and clinical performance of an automated immunoassay for serum cardiac troponin I (Bayer Immuno 1™, Bayer Diagnostics, Tarrytown, NY). the between batch imprecision was found to be between 1.2 and 3.2% over the concentration range 2.5-34.0 μg/L. the analytical range obtained from duplicate analysis of patient samples and defined as a coefficient of variation of 10% or less was 0.3 - 200 μg/L. the detection limit was found to be less than 0.1 μg/L. A method comparison with the Dade Stratus method (Dade Behring, Wilmington, DE) yielded regression statistics with a slope of 0.705 and an intercept of -0.260. an analysis of samples from 40 patients with renal failure demonstrated six with detectable levels of troponin I (0.2-1.9 μg/L). Samples from patients with paraproteinaemia did not demonstrate detectable troponin I (from n = 30); however, two patients with elevated rheumatoid factor titers (from n = 20) demonstrated a detectable amount of troponin I (0.1 and 0.2 μg/L). in a study of 100 patients admitted with acute chest pain and a diagnosis of unstable angina, 6 were subsequently diagnosed as having suffered a myocardial infarction. on admission the sensitivity and specificity of the troponin I results were 26.7% and 94.7%, respectively, moving to 100% and 83% 12 hours after admission.