To clarify the relationship between insulin resistance and QTc interval, we measured QTc interval and HbA1c before and8weeks after troglitazone (TRO, 400mg/day) or voglibose (0.6mg/day) treatment in 24patients with non-insulin dependent diabetes mellitus. No significant change in the QTc interval was observed in either group, but the ΔQTc [=QTc (after TRO) QTc (before TRO)] correlated significantly with the ΔHbA_1c [=HbA_1c (after TRO)-HbA1c (before TRO)] in the TRO group (r=0.606, p<0.05). These results suggest that TRO may shorten the QTc interval in non-insulin dependent diabetes mellitus