We developed a new system to monitor glucose continuously in vivo. The miniaturised system is very easy to handle and was optimised to a resource-saving working modus. Sampling was performed by means of a biocompatible microdialysis needle probe inserted into the subcutaneous tissue. During glucose tolerance tests the results of our monitoring system were correlated with the glucose level of the venous blood stream. A comparison according to the procedure known as 'error grid analysis' provided an excellent correlation between the two completely independent analyses systems with the reference determination results. All values obtained with our systems were clinically correct or at least clinically acceptable.