The considerable disagreement in the definition of impaired glucose tolerance (IGT) by National Diabetes Data Group (NDDG) and World Health Organization (WHO) criteria was explored in two independent representative adult population samples in Israel (n = 1119) and the United States (n = 1783). Five categories of nondiabetic glucose tolerance were defined according to fasting plasma glucose (FPG) values (mM) and 1- and 2-h plasma glucose values (PG1 and PG2, respectively) after oral glucose load: 1) normal by WHO and NDDG (FPG less than 6.4 mM, PG1 less than 11.1 mM, PG2 less than 7.8 mM), 2) Normal by WHO, nondiagnostic by NDDG (FPG 6.4-7.7 mM, PG1 less than 11.1 mM, PG2 less than 7.8 mM), 3) normal by WHO, nondiagnostic by NDDG (FPG less than 7.8 mM, PG1 greater than or equal to 11.1 mM, PG2 less than 7.8 mM), 4) IGT by WHO, nondiagnostic by NDDG (FPG less than 7.8 mM, PG1 less than 11.1 mM, PG2 7.8-11.0 mM), and 5) IGT by WHO and NDDG (FPG less than 7.8 mM, PG1 greater than or equal to 11.1 mM, PG2 7.8-11.0 mM). Established markers of abnormal glucose tolerance were also measured, including glycosylated hemoglobulin A1, insulin response, plasma triglycerides, serum uric acid, and rate of hypertension in Israel as well as rates of hypertension, peripheral vascular involvement, family history of diabetes, and history of cholelithiasis in the U.S. Accounting for potential confounders, levels of these markers in both national samples were similar in categories 1 and 2 and in categories 3-5.(ABSTRACT TRUNCATED AT 250 WORDS)