Therapeutic manipulations designed to conserve myocardium in patients with acute myocardial infarction appear to improve prognosis. To assess the role of glucocorticoids given in pharmacologic dosage in the early treatment of patients with acute myocardial infarction, serial serum creatine phosphokinase (CPK) were obtained every 1–2 hours in 39 consecutive patients admitted with acute myocardial infarction. Determination of completed infarction size (ISc) was made using all available CPK values (range 70–160 hours). Predicted infarct size (ISp) was based on early data following the rise in CPK from baseline values; projected CPK values were obtained over a 160 hour period using a curve fitting procedure based upon non-linear Gauss-Newton stepwise iterations. In 13 uncomplicated control patients ISp was 43.2 ± 11.6 (mean ± SE) CPK-gramequivalents (CPK-g-eq), based on data from the first 7 hours following the rise in serum CPK, while ISc was 44.7 ± 11.4 CPK-g-eq (r = .99, n = 13). In 7 additional control patients whose hospital courses were complicated by clinical extension ISp was 71.8 ± 18.0 CPK-g-eq while ISc was 118.6 ± 31.0 CPK-g-eq (p < .03). In 19 patients treated with 2 grams of methylprednisolone 7–14 hours following the rise in serum CPK from baseline, data from early CPK determinations (7 hours) indicated an ISp of 118.5 ± 24.1 CPK-g-eq while total CPK data indicate an ISc of 89.6 ± 13.2 CPK-g-Eq (p < .04). The exponential clearance of CPK (kd) was approximated in the controls (kd = .00095 ± .00007 min−1) and glucocorticoid treated patients (kd = .00099 ± .00006 min−1) and found to be similar. Thus, administration of a pharmacologic dose of methylprednisolone 7–14 hours following rise in serum CPK from baseline in a group of patients with acute myocardial infarctions has resulted in salvage of myocardium.