Pancreatic sections from diverse tetrapods, including various species of caviomorph rodents, were immunohistochemically investigated using two antisera which reacted with the N- and C-terminal portions of the glucagon molecule. While the antiserum against the N-terminal portion stained alpha cells in all the species studied, the antiserum against the C-portion failed to stain alpha cells in two caviomorphs of the Caviidae family (guinea pig and cuis) and in one of the Octodontidae family (degu). The observations in guinea pig and degu were expected, since their glucagons differ from those of many other tetrapods in the C-terminal portion of the molecule. In this paper, the cuis was added to these two species. It is noteworthy that among the caviomorphs studied herein (nine species), immunohistochemical differences were detected only in the three above-mentioned species and did not involve higher taxa, thus suggesting that these modifications are relatively recent in the evolution of this group of rodents.