The insulin delivery rates were estimated in 8 normal and 8 diabetic subjects from the results of peripheral insulin response to a single bolus iv injection of glucose, taking account of fractionally removed insulin. The delivered insulin response to 0.5 g/Kg body weight of glucose injection was biphasic in normal and diabetic subjects. In normal subjects, 1.7 +/- 0.3 U of insulin was delivered during the first phase (0-10 min) and 5.6 +/- 1.6 U during the second phase (11-60 min). In diabetic subjects, 0.4 +/- 0.2 U of insulin was delivered during the first phase and 1.8 +/- 0.5 U during the second phase. The amounts of delivered insulin during the first and second phases were significantly decreased in diabetics (p less than 0.01). The insulin delivery rates during the first and second phases fitted by the same line to the glucose concentration at each period. This suggests that a common glucoreceptor or glucose-mediated signal of the insulin response might exist during both phases. The glucose-insulin response curves in mild diabetics seemed to be similar to those in the normals, but shifted toward higher glucose levels. This finding suggests that the decreased glucose sensitivity of pancreatic beta cells in mild diabetics can be corrected by high glucose concentrations.