A gelatin capsule is widely used as a device for oral administration of granular/powdered materials or small amounts of liquid materials in animal experiments. In this study, we investigated the insulin- and glucagon-related parameters following oral administration of gelatin capsules to beagle dogs since a gelatin capsule is made of protein composed of many amino acids as known to stimulate insulin or glucagon secretion. Gelatin capsules (1/2 ounces in size) were administered once orally to three male beagle dogs at the dose level of 0.29 and 1.67 g/kg as gelatin and the plasma levels of insulin, glucagon, glucose, non-esterified fatty acids (NEFA), total ketone bodies (KB) and alanine were determined before dosing and for up to 4 hr after dosing. Plasma insulin, glucagon and alanine levels increased immediately after dosing and subsequently plasma NEFA and total KB levels decreased. Most of these changes disappeared by 4 hr after dosing. No effects on plasma glucose levels were noted. In conclusion, a single oral administration of gelatin capsules increased plasma insulin and glucagon levels transiently and altered plasma levels of some biochemical parameters in dogs. These results might imply that attention should be paid to their own effect on the insulin and glucagon secretion at conducting animal experiments using a lot of gelatin capsules.