The research topic of glutamine use in critically ill patients is currently quite controversial. It is not clear whether its use is safe and effective. In our study, we focused on whether plasma glutamine concentration varies in patients with SIRS (systemic inflammatory response syndrome), sepsis, severe sepsis, and septic shock compared to the control group. At the same time, we investigated if glutamine could be used as a prognostic factor in predicting the outcome of disease. Analyzes were performed using a gas chromatography –mass spectrometry in which patient samples were analyzed. The final results confirmed our assumption, that glutamine concentration changes in relation to the disease state. The results of the study confirm that there is a decrease in glutamine concentration in the blood in those patients where the organism is still able to react appropriately to infection and there is no organ dysfunction present. Increased dysfunction or even failure of the organs that are involved in glutamine metabolism will increase the incidence of severe conditions (severe sepsis and septic shock), which can lead to an increase in glutamine concentration. Plasma glutamine concentrations could thus be used to predict the outcome of disease, where higher plama glutamine levels indicate a less favourable outcome.