We describe a new one-step enzyme immunoassay of troponin T that uses two specific monoclonal antibodies and streptavidin-coated tubes as the solid phase. The monoclonal antibodies were obtained by conventional hybridoma technology, with human troponin T as antigen. The identity of the cardiac troponin T antigen was confirmed by analysis of the amino acid composition and by partial sequence analysis. The specificity of the monoclonal antibodies for cardiac troponin T was proved by immunoblot analysis and displacement curves. The capture antibody is labeled with biotin. The second antibody is conjugated to horseradish peroxidase (EC 1.11.1.7). The assay [Enzymun-TestR system (Boehringer Mannheim GmbH)] is performed in only 90 min at room temperature; the measuring range for troponin T is 0.1 to 15 micrograms/L. The assay shows excellent between-run precision (CV = 3.3-4.9%).