The effects of glucocorticoids on the pancreatic endocrine function was studied in isolated mouse pancreatic islets maintained in tissue culture for 1 to 3 weeks. Following culture for 2 week without corticoid supplement acute experiments with hydrocortisone showed no significant effect on the glucose-induced insulin release at 10(-8) to 10(-5) mol/l hydrocortisone. When, however, the islets were cultured in the presence of hydrocortisone, there was an increased insulin release to the medium in a dose-dependent manner, with the maximal effect at 10(-7) mol/l hydrocortisone. The release of glucagon to the medium was not affected to the same degree, but showed a slight inhibition at increasing concentrations of hydrocortisone. Short-term experiments after the culture period showed that islets cultured for 3 weeks in the presence of 10(-7) to 10(-5) mol/l hydrocortisone had an enhanced insulin secretion in response to glucose. The islets did not show any statistically significant change in their insulin- and DNA-content after 3 weeks of culture with hydrocortisone, but a marked reduction in the content of hydrocortisone. The present results suggest that physiological concentrations of hydrocortisone are importance for mouse islets to maintain their insulin production in tissue culture.