Objectives: Although studies have indicated that adrenal insufficiency occurs after severe trauma and hemorrhagic shock, it remains controversial whether adrenal function is depressed during the late stage of polymicrobial sepsis. Design: Prospective, controlled animal study. Setting: A university research laboratory. Subjects: Male rats (275-325 g) were subjected to polymicrobial sepsis by cecal ligation and puncture (CLP) or sham operation followed by the administration of normal saline solution. Measurements and Main Results: Systemic blood samples were taken at 20 hrs after CLP (i.e., a late stage of sepsis) or sham operation to measure plasma levels of corticosterone and corticotropin as well as adrenal contents of corticosterone. Additional groups of animals were utilized to examine corticotropin-stimulated plasma corticosterone release as well as adrenal levels of cyclic adenosine monophosphate (cAMP, the second messenger of corticotropin action). The results indicate that despite a 75% (p < .05) higher concentration in plasma corticotropin at 20 hrs after the onset of sepsis, plasma corticosterone levels were similar to those in sham-operated animals. In addition, adrenal contents of corticosterone were reduced by 42% (p < .05) in septic animals. Moreover, the plasma corticosterone and adrenal cAMP responses to corticotropin were reduced by 53% and 27% (p < .05), respectively, at 20 hrs after CLP. Conclusions: These findings suggest that, despite high plasma levels of endogenous corticotropin, adrenal dysfunction, as indicated by the reduction of corticotropin-induced plasma corticosterone release and adrenal contents of cAMP as well as the decreased adrenal levels of corticosterone, occurs during the late stage of polymicrobial sepsis. Therefore, the recognition of adrenal insufficiency and interventions to improve adrenal responsiveness may be beneficial in improving the outcome during late sepsis.