Thoracic pain is one of most frequent reasons for consultations at an Emergency Unit. Clinical description and the ECG are fundamental for its analysis, but a serious diagnostic problem arises when these do not provide typical data. Our aim is to analyse recently introduced biochemical parameters in order to test whether it is possible to discriminate between entities that are associated with myocardial necrosis and those others in which necrosis is due to striated muscle.We analysed troponin-I and the relation between CPK-MB and total CPK in the serum of 45 patients who attended the Emergency Services with different processes of striated muscle in whom the total CPK was elevated, and 50 patients with acute myocardial infarct. The serum was analysed through an immunotest by fluorescence with monoclonal antibodies.Troponin-I proved to be above the normal value in the 50 patients with myocardial infarct an in 4 of the 45 in the muscular group. The total CPK/MB/CPK ratio was significantly higher in the infarct group than in the muscular group. In all of the patients of this latter group the relation was less than 5%.Troponin-I rises above the normal value and is very sensitive in a myocardial infarct. The total CPK/MB/CPK relation discriminates between processes of muscular necrosis (value 5%). The increase of troponin-I supports the diagnosis of myocardial lesion when the pain suggests a coronary origin but the ratio does not reach 5%.