We tested the ability of three potential screening tests for diabetes (fasting plasma glucose value ≥140 mg/dl, 1-h postglucose (PG) load value ≥200 mg/dl, and 2-h PG value ≥200 mg/dl) to detect non-insulin-dependent diabetes in 130 diabetic Mexican Americans (MAs) and 50 diabetic Anglo Americans (AA) usingthe National Diabetes Data Group criteria as the standard. The sensitivity of the fastingplasma glucose (FPG) cutpoint in detecting diabetes was low in both AAs (36.0%) and MAs (59.3%) and was related to the age-adjusted prevalence rates of diabetes in the two ethnic groups (AAs, 4.9% MAs, 10.9%). The 2-h PG load cutpoint had good sensitivity (> 93%) and specificity (> 99%) in both ethnic groups. The ethnic difference in the sensitivity of the FPG cutpoint appeared to be related to the greater hyperglycemia of diabetic MAs compared with diabetic AAs. Nearly 30% of diabetic MAs had FPG values ≥ 200 mg/dl as contrasted with only 10% of diabetic AAs. The difference in severity of hyperglycemia between the ethnic groups appears to be unrelated to ethnic differences in adiposity, pharmacologic treatment, or delay in diagnosis, although longer disease duration in MAs may explain part of the difference.