We describe a computer program based on the minimal model of Bergman et al., which has been used to control euglycaemic hyperinsulinaemic clamps and to derive the insulin sensitivity index (Si) from clamp data. Clamps were undertaken on 33 subjects with a range of insulin resistance. The steady state glucose had an acceptable coefficient of variation (c.v.) and was close to the desired clamp level. The c.v. of the steady state glucose infusion rate was smaller than for other clamp programmes. The Si was correlated with metabolic clearance rate for glucose (MCR) divided by the change in insulin concentration. Our results suggest that the assumptions of the minimal model hold true in the euglycaemic hyper-insulinaemic situation and demonstrate that a minimal-model-derived program can achieve acceptable clamping.