Plasma lipids and lipoproteins usually undergo several phasic changes following myocardial infarction. Within a few hours the free fatty acid (FFA) concentration rises precipitously and may not become normal for 2 days or more. During the first 1 to 3 days, there begins a significant decline in cholesterol and beta lipoproteins. After a possible early decline, the concentrations of very low density lipoproteins and triglycerides begin to climb within the first week and characteristically are considerably above the measured initial levels for weeks thereafter. Beta lipoprotein concentrations return slowly to initial values. The late return of lipids to supranormal levels is probably often an expression of abnormality present before infarction. Some of these oscillations in lipid and lipoprotein concentrations occur after other forms of trauma. Arguments are presented that the early alterations are not attributable to caloric deprivation or anticoagulants and the mechanisms involved are speculated upon.