OBJECTIVES: The stress response involves the activation of the hypothalamic-pituitary-adrenal(HPA) axis and the sympathetic nervous system. Corticosteroids have been clearly demonstrated to cause anti-inflammatory and/or immnosuppressive effects in man including granulocytosis in part by decreasing migration into tissue, especially damaged tissues(myocardium), and circulating relative lymphocytopenia. To test whether automated measurements of the the increased serum cortisol-induced hematologic changes in the leukocyte differential significance or not in the initial differential diagnosis of acute myocardial infarction in acute chest pain syndromes. METHODS: 101 consecutive patients with myocardial infarction or myocardial ischemia presenting to the emergency room of Seoul Adventist Hospital with acute chest pain from January 1993 to August 1995(Retrospective group) and from December 1995 to March patients compatible with exclusion criteria in myocardial infarction were excluded. We measured automated leukocyte differential and serial CK-MB level in both groups, and the intial serum cortisol levels in prospective infarction group. RESULTS: 1) Total leukocyte and granulocyte counts were increased in acute myocardial infarction(p<0.01). 2) In acute myocardial infarction group, lymphocyte counts were slightly increased(p<0.05), but relative lymphocytes percentage more significantly decreased(p<0.01). 3) Serum cortisol levels are significantly raised early in the course of the acute myocardial infarction and prior to the elevation of the specific cardiac enzymes on the basis of analytic results of prospective infarction group. 4) Cortisol-induced changes in leukocyte differential were noted with time passes into reverse approximately 4 days later in our study. 5) The leukocyte differential does not shows significant changes in the retrospective myocardial ischemia group, so we arrive in careful conclusion that serum cortisol level seems does not increase. 6) No sexual differences were noted in leukocyte differential. CONCLUSIONS: The serum cortisol level and cortisol-induced leukocyte differential are helpful for initial differential diagnosis of acute myocardial infarction in acute chest pain sysdrome.