The objective of the study was to develop and evaluate a portable device for continuous fractionated blood sampling and continuous ex vivo monitoring of blood glucose. The inner lumen of a double lumen catheter (18 gauge x 45 mm) was placed in a peripheral vein and perfused with heparin solution (1.4 U min-1). The outer lumen was used to collect heparinized blood into 48 vacuum tubes at programmable sample volumes and time intervals (0.2-2 ml in 2.5-30 min). A sensor flow chamber with an internal volume of 1 mm3 incorporating a miniaturized thin-film amperometric glucose sensor was placed in the sampling line for continuous ex vivo blood glucose monitoring. Blood glucose and plasma insulin were measured during a frequently sampled intravenous glucose tolerance test (250 mg kg-1) and a subsequent oral glucose tolerance test (150 g) over 6 h in eight healthy volunteers (BMI 24.5 +/- 3.2 kg m-2). Additionally, in four experiments blood glucose was measured on-line using the glucose sensors. The overall correlation coefficients for whole blood glucose and plasma insulin between the manually drawn samples and the vacuum tubes were 0.73 and 0.87, respectively (p < 0.001). The miniaturized glucose sensor exhibited a linear measuring range of 25 mmol-1 glucose concentration and 95% response times of less than 30 s. Sensor readings and laboratory analyser results for the blood glucose measurement correlated between 0.93 and 0.98 (p < 0.001). In summary, continuous fractionated blood sampling and ex vivo blood glucose monitoring in ambulatory subjects is possible with a portable device.