The purpose of this paper is to develop a microdialysis probe with higher recovery for continuous sensing of glucose concentration in subcutaneous tissue. The value for the mass transfer coefficient obtained by in vivo experiment is compared with that by in vitro experiment. Optimum conditions for fast response and high recovery are determined as a perfusion rate of 120 mu l . h(-1) and a probe length of 15 mm using regenareted cellulose capillary membrane. The relationship between the glucose concentration in blood and the glucose concentration in subcutaneous tissues was examined by inserting probes underneath the skin, and perfusing a dialysate of different glucose concentrations. The glucose concentration in subcutaneous tissues is found to be almostly consistent with that in blood. The mass transfer coefficient external to the probe in subcutaneous tissues, k(ext) = 1,2 similar to 2.4 mu m . s(-1), is 20 similar to 50% of the values of those obtained by in vitro experiments (k(ext) = 5.7 similar to 6.7 mu m . s(-1)).