Products for monitoring blood glucose that allow extraction from sites other than the finger have recently been introduced. The FreeStyle Blood Glucose Monitor requires only 0.3 microL of blood, and allows extraction from the hand, arm, and leg, as well as the traditional finger site. Differences in circulatory physiology of the off-finger test sites lead to differences in the measured blood glucose concentration. The first study involved 160 clinic visits by 120 unique subjects with type 1 or type 2 diabetes. FreeStyle measurements were compared to YSI Model 2300 Stat Plus Glucose Analyzer plasma measurements using venous blood, capillary blood from the finger, and capillary blood from the arm. In a second study, the time course of glucose variation was tested by simultaneous measurements on the arm and finger taken every 15 min for 6 h. Thirteen subjects with type 1 diabetes were studied in two 6-h sessions. When FreeStyle was compared to YSI using venous samples and finger samples, the regression statistics were very similar. But when FreeStyle with arm samples was compared to YSI with finger samples, the regression equation was similar, but the scatter in the data was statistically significantly greater at the 95% confidence interval. By studying the time course of glucose changes, the difference between finger and arm measurements was attributed to a time lag in the glucose response on the arm with respect to glucose response on the finger. The lag was observed when the glucose concentration was increasing or decreasing, and the lag time varied from subject-to-subject in the range of 5-20 min. Using the Clarke Error Grid Analysis, the difference between arm and finger glucose measurements was not clinically significant. However, when the glucose concentration is decreasing rapidly into a state of hypoglycemia, the lag in measurements on the arm could delay detection of hypoglycemia. When specifically testing for hypoglycemia, the finger may be the preferable test site.