Polymorphonuclear neutrophils (PMN) are known to participate in the development of tissue injury during myocardial infarction due to both free oxygen radicals release, as well as to their involvement in the "no-reflow" phenomenon. We have previously shown that peripheral blood plasma (obtained from patients with acute myocardial infarction) has chemotactic activity for PMN and is able to induce PMN adherence as well as superoxide anion production. To investigate whether interleukin-8 (IL-8/NAP-1), a potent chemotactic factor for PMN, is involved in plasma-mediated PMN stimulation, we measured plasma levels of IL-8 in five patients with transmural myocardial infarction with highly sensitive enzyme-linked immunosorbent assay (ELISA) using specific antibodies. Blood samples were taken immediately after patients' admission, within 15 and 30 min of treatment with intravenous nitrates, as well as after 1, 2, 3, and 7 days. All samples expressed IL-8 activity within the detection limit (0.4 ng/ml) as observed at the basal state. Thus, IL-8 may not be considered as responsible for the chemotactic activity in peripheral blood in patients with myocardial infarction.