The sequential changes of Lp(a) lipoprotein concentrations in patients (n = 59) suffering acute myocardial infarction (AMI) were examined and compared with other plasma proteins. The temporal and quantitative characteristics of the responses in concentration of acute phase reactants (CRP, haptoglobin, alpha 1-antitrypsin, alpha-acid glycoprotein), lipids (total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol) and apolipoproteins AI and B were similar to previous reports. Lp(a) lipoprotein showed transient changes with an initial decrease of 10-25% compared to the 3-month control value, followed by rebound on day 7-11 above admission level, before again declining. We were able to demonstrate a quantitative relationship between infarct size and alterations in plasma levels of acute phase reactants. However, in addition to rather unusual significant fluctuations during AMI, Lp(a) lipoprotein changes seemed unrelated to infarct size. These findings do not support the view that Lp(a) lipoprotein acts as an acute phase reactant.