Insulin resistance in type 2 diabetes subjects was investigated before and 6 months after insulin administration in 43 type 2 diabetes patients (28 females and 15 males). Their age was 56.1±8.6 years, diabetes duration 11.7±6.8 years, BMI 29.5±5.3kg/m². All patients were on maximal dosage of oral hypoglycaemic agents and had poor metabolic control (HbA1_c 11.2±1.6%). Insulin sensitivity was measured by euglycaemic clamp (insulin infusion rate 1mUkg⁻¹min⁻¹). The glucose disposal rate (M-value) was considerably lower in patients (2.4±1.6mgkg⁻¹min⁻¹, 0.2–8.1) compared with healthy subjects (7.1±0.2mgkg⁻¹min⁻¹, p<0.01). M-value was strongly associated with WHR (r=−0.41, p<0.05). The patients with poorest insulin sensitivity had the highest level of total cholesterol (r=−0.41, p=0.02) and LDL-cholesterol (r=−0.38, p=0.03). After 6 months of insulin treatment BMI was 30.3±4.2kg/m² (p<0.05), mean weight increase was 2.7±0.8kg. M-value was substantially increased to 4.5±2.3mgkg⁻¹min⁻¹ (p<0.001), the degree of improvement depended on basal insulin sensitivity (r=−0.55, p<0.01). HbA1_c was reduced to 7.7±1.4% (p<0.01), the correlation M-value with change of HbA1_c (r=−0.59, p<0.01) was shown. Total cholesterol decreased from 6.3±1.1 to 5.4±1.1mmol/l, LDL-cholesterol from 4.1±1.1 to 3.4±1.0mmol/l, triglycerides from 2.6±1.6 to 1.6±0.7mmol/l (p<0.001). In conclusion, insulin treatment of type 2 diabetes patients leads to decrease in insulin resistance due to reduction in glucose toxicity and plasma atherogenicity despite weight gain.