Objective To evaluate islet β cell response to intravenous glucagon（a non-glucose secretagogue）stimulation in diabetes mellitus.Methods Nineteen patients with type 1 diabetes（T1D）and 131 patients with type 2 diabetes（T2D）were recruited in this study.T2D patients were divided into two groups according to therapy:36 cases treated with insulin and 95 cases treated with diet or oral therapy.The serum C-peptide levels were determined at fasting and six minutes after intravenous injection of 1 mg of glucagon.Results Both fasting and 6-minute post-glucagon-stimulated C-peptide levels in T1D patients were significantly lower than those of T2D patients（0.76±0.36 ng/mL vs.1.81±0.78 ng/mL

P<0.05;0.88±0.42 ng/mL vs.3.68±0.98 ng/mL

P<0.05）.In T1D patients

the C-peptide level after injection of glucagon was similar to the fasting level.In T2D

patients treated with diet or oral drug had a significantly greater fasting and stimulated C-peptide level than those patients received insulin therapy（2.45±0.93 ng/mL vs.1.61±0.68 ng/mL

P<0.05;5.26±1.24 ng/mL vs.2.15±0.76 ng/mL

P<0.05）.The serum C-peptide level after glucagon stimulation was positively correlated with C-peptide levels at fasting in all three groups（r=0.76

P<0.05）.Conclusions The 6-minute glucagon test is valuable in assessing the function of islet β cell in patients with diabetes mellitus.It is helpful for diagnosis and treatment of diabetes mellitus.