The aim of the paper was assessing the influence of polarizing GIK mixture on the selected indicators of acid-base equilibrium in patients with acute myocardial infarction treated fibrinolytically. The patients had arterial blood taken in order to check pH, partial pressure of oxygen and carbon dioxide, and the content of bicarbonates. Changes in the examined parameters in the group obtaining GIK and in the one obtaining placebo were subject to critical analysis. Changes in gasometric parameters taking place under the influence of GIK administered to patients were also analysed according to the site of infarction. It was observed that after 24 hours from the beginning of infusion pH increased and pCO2 decreased in comparison to the initial examination. These changes did not depend on the kind of applied infusion (GIK or physiological saline infusion), no significant changes in bicarbonates being observed. However, after applying GIK infusion, an increase in oxygen pressure in comparison with the control group was observed, and differences between the groups were within the boundaries of significance. Neither was there observed any influence of infarction site on changes in the assessed parameters of acid-base equilibrium in the group treated with GIK nor in the one receiving placebo.