The glucose concentration in the extracellular space of subcutaneous adipose tissue closely mirrors the blood glucose concentration. With a microdialysis technique, we undertook continuous ambulatory monitoring of adipose tissue glucose in 17 insulin-dependent diabetic patients with labile glycaemic control. The aims of the study were to investigate performance of the microdialysis device and to evaluate whether consecutive 24 h glucose profiles could be used to adjust insulin therapy. A microdialysis probe was implanted subcutaneously, perfused by a portable microinfusion pump, and dialysate fractions were collected every 1 or 2 h for 75 h. The mean (SE) tissue dialysate glucose concentration was 93 (3)% of the concentration in venous plasma, and variations in adipose tissue glucose closely paralleled changes in plasma glucose. Mean 24 h tissue glucose concentration correlated significantly with glycosylated haemoglobin (HbA1c; r = 0.62, p < 0.01). Most patients had a reproducible daily pattern of glucose swings, and in more than half the patients consecutive ambulatory glucose profiles were almost superimposed. When patients' insulin therapy was adjusted on the basis of ambulatory glucose monitoring, HbA1c decreased by almost 2% (p < 0.01), and this decrease lasted for at least 9 months. Microdialysis of adipose tissue can be used for continuous long-term monitoring of glucose concentrations in diabetic patients during ordinary daily life. Daily glucose profiles are often reproducible and the recordings may thus be used for individual tailoring of insulin therapy to improve glycaemic control.