The relationship between post-prandial plasma glucose (PPG) and post-challenge plasma glucose (PCG) within individuals was investigated in Japanese population. The oral glucose tolerance test (OGTT) and measurements of PPG 2h after ingestion of a standardized rice-based meal (PPG2h), were performed in 4471 middle-aged Japanese subjects (2774 men and 1697 women, 50.7+/-8.5 years). There was a loose correlation between PPG2h and PCG2h (r=0.327, p<0.001). The diabetes group (n=170) showed the highest PPG2h, followed by the IGT group (n=786) and the NGT group (n=3414) (p<0.05). At the cutoff point of 140 mg/dl (7.8 mmol/l) for PPG2h, specificities were 94.9% for IGT plus diabetes and 92.9% for diabetes, but sensitivities were as low as 23.2% for IGT plus diabetes and 44.7% for diabetes. The correlation of PPG2h with PCG2h was stronger in the obese group (BMI>or=25 kg/m2) than in the lean group (BMI<20 kg/m2). We conclude that the correlation between PPG2h and PCG2h was significant but not very tight. In evaluating PPG2h, if the cutoff point of 140 mg/dl (7.8 mmol/l) for PCG2h is extrapolated, the majority of subjects with dysglycemia could be overlooked.