To evaluate the superiority of insulin glargine as basal insulin replacement by continuous glucose monitoring system (CGMS). Twenty-four patients with type 2 diabetes mellitus (T2DM) whose blood glucose was not well controlled with sulphanylureas were enrolled. At first, they were treated with extended-release glipizide (glucotrol XL) 5mg/d before breakfast for 2 weeks, then randomized to combination treatment with glargine (16 patients) or NPH (8 patients) and treated for 12 weeks. CGMS were carried in the second week after treatment with glucotrol XL, and in the 12th week after combination treatment. The data of CGMS showed: (1) When FPG were well controlled in both groups (glargine group versus NPH group: 6.0+/-1.0 mmol/L versus 5.8+/-1.3 mmol/L), the blood glucose level at 3:00 a.m. (5.1+/-0.9 mmol/L versus 4.2+/-0.8 mmol/L) were higher (P<0.05), TPG< or =3.0 mmol/L at night were lower (2.56+/-1.79 versus 5.88+/-1.96), and the rate of nocturnal hypoglycemia (1/16 versus 4/8) were less (P=0.028) in glargine group than those in NPH group. (2) CGMS showed that the daily blood glucose profile excursion were more smoother in glargine group than those in NPH group. In conclusion, it was confirmed with CGMS that compared with traditionally basal insulin replacement with NPH, the combination treatment with glargine injection at bedtime may be predominant for stabilizing the daily blood glucose profile excursion and decreasing the nocturnal hypoglycemia events incidence. So glargine may be a more ideal basal insulin replacement than NPH.