Although glucagon-like peptide-1 has the appearance of a glucagon-homologue that may be co-secreted with glucagon, synthetic glucagon-like peptide-1-(1-37) does not significantly affect plasma glucose and insulin concentrations when administered at high doses (100 and 400 micrograms) to cortisone-pretreated rabbits. This synthetic preparation thus lacks the primary metabolic effect of glucagon at the doses tested. An intra- or extra-pancreatic role of glucagon-like peptide-1 has yet to be discovered.