Recent data confirmed that the chronic mild stress (CMS) model of depression has high validity. In our study, decreases in reactivity to rewards in rats following exposure to CMS were observed. The aim of the present study was to investigate the changes of the daily hormonal levels following CMS alone or in combination with various lighting schedules and to analyse the rhythm parameters. 102 adult rats of both genders were randomly distributed in the following groups: 1) controls, 2) using CMS under different lighting regimens and 3) repeated shifts of the lighting regimen without CMS. Sucrose consumption was measured weekly. The plasma corticosterone in the female CMS group kept in LD schedule was slightly decreased during the light phase compared to the control group kept in LD, and slightly elevated during the dark phase, but not in males. The observation that no statistically significant difference in circadian rhythm characteristics was found between the CMS-stressed and non-stressed animals is an indication that the load associated with lighting schedule shifts may have been harder than the CMS procedure, at least from the viewpoint of maintaining an integral circadian time structure. Mean values showed a significant reduction of testosterone of the CMS-treated male rats as compared to controls. Circadian rhythm was demonstrated for testosterone for the CMS-stressed animals but not for the non-CMS-stressed rats. In conclusion, CMS and also disturbing lighting schedule itself result in the impairment of certain hormonal rhythms and these disturbances appear in an early stage of anhedonic behaviour. Support: ETT314/2006.