In phenotype experiments in mice, determination of dynamic insulin sensitivity often uses the insulin tolerance test. However, the interpretation of this test is complicated by the counterregulation occurring at low glucose. To overcome this problem, we have determine the dynamic insulin sensitivity after inhibition of endogenous insulin secretion by diazoxide (25mg/kg) in association with intravenous administration of glucose plus insulin (the DSGIT technique). Estimation of insulin sensitivity index (S_I) by this technique showed good correlation to S_I from a regular intravenous glucose tolerance test (r=0.87; P<0.001; n=15). With DSGIT, we evaluated dynamic insulin sensitivity in mice with a beta cell targeted dominant-negative mutation of hepatic nuclear factor (HNF)-1(RIP-DN HNF-1 (Tg) mice). When insulin was administered exogenously at the same dose in Tg and wildtype (WT) mice, plasma insulin levels were higher in WT, indicating an increased insulin clearance in Tg mice. When the diazoxide test was employed, different doses of insulin were therefore administered (0.1 and 0.15 U/kg in WT and 0.2 and 0.25 U/kg in Tg) to achieve similar insulin levels in the groups. Minimal model analysis showed that S_I was the same in the two groups (0.78±0.21 [10^-4 min^-1/(pmol/l] in WT vs. 0.60±0.11 in Tg; P=0.45) as was the glucose elimination rate (K_G)(P=0.27). We conclude that (i) the DSGIT technique determines the in vivo dynamic insulin action in mice, (ii) insulin clearance is increased in RIP-DN HNF-1 mice, and (iii) chronic islet dysfunction in RIP-DN HNF-1 mice is not compensated with increased insulin sensitivity.