Subcutaneous adipose tissue extracellular glucose was investigated in vivo in man with a microdialysis technique. A small dialysis probe (4 or 10 x 0.5 mm) was implanted subcutaneously, and was perfused continuously with a micro-infusion pump. Dialysate samples were collected in 15-min periods. A transient yield of ATP was recorded immediately after insertion of the probe; thereafter ATP was almost undetectable. During steady-state conditions the tissue dialysate glucose concentration remained constant for at least 2 h, which indicated that there was no drainage of glucose from the interstitial fluid to the tissue dialysate. Simultaneous dialysis of venous blood and subcutaneous fat in rats showed that the recovery of glucose from the adipose tissue interstitial fluid to the dialysate was only 20% of that from blood. However, in vivo dialysis of human adipose tissue with glucose-containing solutions produced an equilibrium with the extracellular space at a glucose concentration that was similar to the blood glucose concentration. After oral glucose ingestion and following i.v. insulin and glucose administration the relative variations in subcutaneous glucose closely resembled those in blood glucose. It is concluded that the subcutaneous implantation of the presently used small dialysis device causes only minor and transient traumatic effects. The dialysis recovery of glucose is lower in adipose tissue than in blood. However, the relative kinetics of subcutaneous tissue dialysate glucose are closely related to variations in the blood glucose concentration, and thus may be used for monitoring of glycaemic control in man.