OBJECTIVES To study homocysteine (Hcy) levels during post-infarction follow-up. METHODS AND RESULTS In this study, serum Hcy levels were measured in 90 healthy individuals and in 127 patients with acute myocardial infarction (MI) on the day of infarction (day 0) and days 2, 5, 7, 9, and 11 post-infarction, comparing Hcy levels in MI patients on day 0 with their follow-up results and with levels in controls. Overall, MI patients had higher Hcy levels on day 0 versus controls. However, the behavior of Hcy levels differed between two groups of MI patients. Thus, patients with similar Hcy levels to controls on day 0 showed significantly higher levels on days 2, 5, 7, 9, and 11 post-infarction than on day 0. In contrast, patients with significant higher Hcy levels than controls on day 0 showed significantly lower levels on days 2, 5, 7, 9, and 11 post-infarction than on day 0. CONCLUSIONS Different behaviors of Hcy levels in MI patients might correspond to a history or absence of history of asymptomatic myocardial ischemia. Further research is required to test this hypothesis.