This study investigated the glucagon-releasing properties of the hormones glucagon-like peptide-2 (GLP-2) and glucose-dependent insulinotropic polypeptide (GIP) in 8 patients with type 1 diabetes mellitus (T1DM) without paracrine intraislet influence of insulin (C-peptide negative following a 5 g intravenous arginine stimulation; on study days only treated with basal insulin substitution). On 3 study days, 180-minute two-step glucose clamps were performed. Plasma glucose (PG) was clamped at fasting values, with a mean of 7.4+/-0.5 mM in the first 90 min (period 1) and raised 1.5 times the fasting values to a mean of 11.1+/-0.1 mM in the last 90 min (period 2). In randomised order either GIP, GLP-2, or saline were infused intravenously during first 50 min in both periods at rates designed to mimic postprandial hormone responses. The resulting incremental area under curve values of glucagon were in period 1 -38+/-44 (GIP), 120+/-48 (GLP-2), and -16+/-61 (saline) pMx90 min (p=0.087), respectively; and in period 2 -157+/-76, 135+/-52, and -77+/-77pMx90 min (p=0.019), respectively. Post hoc analysis showed significant differences only between the GLP-2 days versus the GIP and saline days. In conclusion, GLP-2, but not GIP, was found to stimulate the release of glucagon in patients with T1DM, suggesting a role for GLP-2 in the postprandial hyperglucagonaemia characterising individuals with T1DM.