Acute exposure to ethanol induces a stress response in mice that is manifested by increased plasma corticosterone (PC) concentration. However, during chronic intake of 7.5% w/v ethanol, diurnal fluctuation of PC is dampened. Whether chronic consumption of 20% w/v ethanol alters normal diurnal fluctuation of plasma glucocorticoids is not known. Investigating the PC response in 20% w/v ethanol-consuming mice is of interest because glucocorticoids are known suppressants of natural killer (NK) cell activity and increased concentration or altered diurnal fluctuation of PC may have a modulatory role on NK cells in these mice. Mice given 20% w/v ethanol for at least 7 days and for as long as 10 weeks have suppressed splenic NK cell cytolytic activity. Thus, the purpose of this study was to examine whether mice given 20% w/v ethanol exhibited normal concentrations and diurnal variation of PC. To further define the glucocorticoid response in chronic ethanol-consuming mice, PC concentration was evaluated in response to a secondary stress of physical exercise. After 1 week, ethanol-consuming mice exhibited abnormal diurnal PC periodicity that was progressively dampened during the remaining 9 weeks. Acute physical exercise during Week 1 induced a 2-fold increase in PC concentration compared with pre-exercise values, a response that was independent of ethanol intake. After 6 and 10 weeks, the postexercise PC concentration was attenuated in ethanol-consuming compared with water-drinking mice. It was concluded that suppressed NK cell activity typically observed with this model of chronic ethanol intake is not directly associated with dampened diurnal fluctuation in PC.