Background: Homeostasis model assessment of insulin resistance(HOMA) had been proposed as a simple and inexpensive alternative to other complex procedures measuring insulin resistance. We evaluated the validity of HOMAIR, comparing to total glucose disposal rate measured by euglycemic clamp test in 63 subjects with normal glucose tolerance, 21 with impaired glucose tolerance and 47 with type 2 DM. Methods: HOMAIR and HOMAβcell function (Homeostasis model assessment of βcell function) were calculated with formula described by Matthews (HOMAIR: fasting insulin (μU/mL) X fasting glucose (mmol/L) / 22.5, HOMAβcell function: 20 X fasting insulin (μU/mL)/(fasting glucose(mmol/L)- 3.5)). 2-hour euglycemic(5mmol/L) hyperinsulinemic (717pmol/L) clamp test were carried out. Results: The strong inverse correlation(r=-0.658, <0.001) was shown between log transformed HOMA and total glucose disposal rates. The agreement of two methodes in the categorization according to insulin resistance was moderate (weighed a =0.45). The magnitude of correlation coefficients were smaller in subjects with lower BMI (BMI < 23.7 kg/m2, r = -0441 vs BMI > 23.7 kg/m2, r = -0.693, p = 0.0183), lower HOMAβcell function (HOMAβcell function 57.2, r = -0.514 vs HOMAβcell function≥57.2, r = -0.773, p = 0.0091) and higher fasting glucose levels (fasting glucose < 102 mg/dL, r = -0.697 vs fasting glucose > 102 mg/dl, r = -0.59, p = 0.0735). The results of correlation analysis was not significant in diabetics with lower BMI. Conclusion: Limitation of validity of HOMAIR should be carefully considered in subjects with lower BMI and lower fasting insulin to glucose levels, such as lean type 2 diabetes with insulin secretory defects (J Kor Diabetes Asso 24:541 551, 2000).