The importance of correct handling of samples for blood gas analysis was studied in 100 patients. Sixty minutes storage in iced water lowered pH by 0.02 pH-units. Storage at room temperature caused considerable changes in PCO2 and PO2 (+0.45 kPa and -1.05 kPa). Air bubbles in the syringes increased PO2 if not expelled within 30 s. Thirty minutes storage with air trapped inside the syringe caused an increase in PO2 of 1.8 kPa and a decrease in PCO2 of 0.16 kPa. The use of plastic syringes induced significant changes in PCO2 and PO2, of which the latter (+1.0 kPa) may be clinically significant. The findings indicate that sample collection and storage must be guarded by strict rules in order to avoid false results.