A comparative study has been made of Pharma-Plast and Arterial-Blood-Sampler-B-109 syringes. Thirty-two syringes were studied in each group: their properties were compared with regard to blood sampling from intravascular catheters with the object of gas level determination. A comparison of the two groups showed no significant difference. It is concluded that there are economic advantages in using the cheaper, simple Pharma-Plast syringes for gas level determination, if the blood is withdrawn from an intravascular catheter. They are particularly recommended for departments carrying out cardiac and vascular surgery, and for scientific projects.