Logistic equation is proposed as a new mathematical model describing the course of the ascending branch of the serum creatine kinase curve: E(t) = K divided by 1 + ea-bt where: E(t) = CK concentration at time t (mU/ml); t = time in hours from the onset of enzyme release; e = natural logarithm base; K = horizontal asymptote of the curve (maximal enzyme activity); a, b = typical variable prameters of the curve. Prediction is based on the identification of the infection point of the ascending branch of the serum CK curve. The enzyme activity corresponding to this point is half of the maximal one. In 14 patients with acute myocardial infarction infarct size (CK-g-Eq) was calculated by the method of Shell et al. In these patients the average differences between observed and predicted parameters were respectively (X +/- SD): -0.64 +/- 2.13 h for the maximal activity time; 16.57 +/- 53.15 mU/ml for the maximal activity and 0.02 +/- 2.44 CK-g-Eq for the infarct size. In detail it can be observed that the average of the per cent differences between observed and predicted infarct size was 1.10 +/- 5.31% and the maximal per cent difference only +10.40%.