This is a mono-centre trial performed at the Center for Clinical Research at the Medical University Graz. There will be a screening information and a study visit.In the study visit arterialized venous blood glucose values will be monitored and subcutaneous sampling of interstitial fluid (ISF) with microdialysis for glucose determination will be performed. Additionally to the laboratory analysis of the subcutaneous glucose samples, the glucose will be measured with extracorporeal on-line sensors and two marketed devices (Guardian RT and Glucoday S).The study visit will last 30 hours starting with the insertion of microdialysis catheters in the abdominal subcutaneous tissue and the insertion of the catheters for the Glucoday S system and Guardian RT system. The primary hypothesis of the study is: Interstitial fluid glucose concentration profiles correlate to the arterialized venous blood glucose concentration profile in type 1 diabetic subjects.