The purpose is to conduct a study on influence of blood sampling systems on indicators of homeostasis. Materials and methods. Indicators of homeostasis were tested with critical care testing systems: GEM Premier 3500, GEM Premier 3500, GEM Premier 3000 (Instrumentation Laboratory, USA), Roche Cobas b 221 (Roche Diagnostic, Switzerland. Arterial blood was used as a sample: system 1: — self-injected heparinized syringe «Inject» (B. Braun, Germany); system 2: — arterial blood collection kit «BD Preset™» («Becton Dickinson and Company», UK). Results. The use of self-heparinized syringes showed significantly lower results of pCO2, K+, Ca++ glucose and lactate values compared to the «BD Preset™». The pO2 values when using syringes were significantly higher than in blood sampling systems. The pH and Na+ values were almost identical when using both systems. Conclusions.The alterations of the results of pCO2, K+, Ca++, Glu and Lac were observed in using of self-heparinized syringes due to preanalytical phase errors such as: non-compliance with the anaerobic conditions for blood sampling, dilution of the sample with liquid heparin. Our study confirms the data available in the literature on the need to use commercial systems for blood sampling systems for the study of homeostasis indicators.