In order to investigate the predictable value of fasting blood glucose (FBG) level for the incidence of non-insulin-dependent diabetes mellitus (NIDDM), 638 nondiabetic subjects who were investigated in 1986 (including 341 subjects with normal glucose tolerance and 297 subjects with impaired glucose tolerance) were reexamined in 1992. The results showed that the 6-year-incidence of NIDDM was significantly increased with rising of baseline FBG level. After adjusting for age, sex and body mass index (BMI), proportional hazard regression analysis showed that FBG level in impaired glucose tolerance group was positively associated with the development of NIDDM (P = 0.0001). Subjects with mean FBG level of 5.19 mmol/L had a higher risk of developing NIDDM than subjects with mean FBG level of 4.61 mmol/L (RR 2.1, 95% CI 1.19-3.74, P = 0.01). The risk ratio of NIDDM was further increased in the group with mean FBG level of 6.l5 mmol/L (RR = 2.9, 95% CI 1.79-4.59, P = 0.0001). The result indicates that FBG level is an independent risk factor for the development of NIDDM.