Female and male mice were fed a laboratory chow (control diet), a high glucose and a high fat diet for three months to test the effects on the pancreatic content of insulin and glucagon. Intravenous glucose tolerance tests showed that the glucose disappearance rate was high in females (p approximately 0.001). Both sexes were equally sensitive to a high fat diet leading to impaired glucose tolerance. A higher body weight was found in both sexes on the high fat diet. Pancreatic insulin and body weight were positively correlated (p approximately 0.009). On all diets, female mice had a higher insulin (p approximately 2.8 x 10(-8)) and a higher glucagon content (p approximately 2 x 10(-10)). By ranking the diets in the following order: control, glucagon and fat the diets decreased the pancreatic insulin content and increased the pancreatic glucagon content. In isolated pancreatic islets from female mice given glucose diet the insulin content was increased by 56 per cent. Female islets had a higher content of both insulin and glucose in comparison to male islets. It is concluded that, independently of differences in dietary composition, female mice have increased glucose tolerance and a higher pancreatic insulin and glucagon content.