A new method for continuous blood collection using the Biostator is described. Blood is withdrawn through the double lumen catheter by a tube installed in the optional channel of the infusion pump. The amount of blood withdrawn from the patient is slightly greater than that necessary for continuous glucose analysis; the excess blood can be collected into assay tubes. Blood collection is continuous and produces a sample of diluted heparinized blood. The volume of blood collected depends on the size of the tube used, i.e. for a tube with a lumen diameter of 0.020 inches, the mean (+/- SD) volume collected was 1.21 +/- 0.07 ml/10 min (n = 13). The mean time interval between sampling and arrival at the glucose sensor by the double lumen catheter was 119 versus 108 s with the conventional method. The proposed modification does not affect blood glucose measurements (correlation coefficient compared with the reference method r = 0.9572; n = 13). To compensate for blood dilution, a dilution-factor depending on tubing diameter has to be calculated in each experiment.