The clinical usefullness of the CPK MB test (spectophotometric method) was evaluated on 139 patients admitted to a Cardiovascular Diseases Department with a diagnosis of suspected myocardial infarction. Serial determinations of serum MB isoenzyme creatine kinase, total creatine kinase, lacate dehydrogenase and hydrossibutirrate dehydrogenase were made at 1st, 2th, 3th, 4th, 5th, 6th, 7th day. Incidence of CPK MB false positive and false negative data were also determined and correlated with the electrocardiogram pattern and serum levels of other standard enzymes. Results indicate that the CPK MB kinetic test is highly specific (94%) and promptly available in the early diagnosis of acute myocardial infarction.