OBJECTIVE: To study the heart rate variability (HRV) and vascular endothelial function in the first degree relatives of type 2 diabetes with normal glucose tolerance (FDRs) and to compare with those of healthy controls. METHODS: HRV, endothelial-dependent vasodilation (EDV) and HOMA insulin resistance index (HOMA-IR) were measured in 37 controls (17 men and 20 women) and 60 FDRs (29 men and 31 women). RESULTS: HRV in FDRs [standard deviation of all normal-normal intervals (SDNN) (124.6 +/- 20.6) ms, standard deviation of average all normal-normal intervals (SDANN) (110.1 +/- 20.1) ms, rate mean square of the differences of successive RR intervals (rMSSD) (33.9 +/- 9.2) ms, low frequency (LF) (1128.5 +/- 314.7) ms(2)/Hz, high frequency (HF) (904.6 +/- 461.6) ms(2)/Hz] was lower than that of the controls [SDNN (140.5 +/- 20.5) ms, SDANN (129.5 +/- 20.3) ms, rMSSD (40.9 +/- 11.4) ms, LF (1678.3 +/- 276.2) ms(2)/Hz, HF(1112.6 +/- 513.7) ms(2)/Hz]. EDV was lower in FDRs than that in the controls [(5.10 +/- 0.14)% vs (12.50 +/- 3.30)%]. HOMA-IR in FDRs was higher than that in the controls (0.57 +/- 0.36 vs. 0.42 +/- 0.23, P < 0.05). CONCLUSIONS: There are increased HOMA-IR, decreased HRV and impaired endothelial function in the FDRs and insulin resistance is positively related with endothelial dysfunction and decreased HRV.