The effect of acute and chronic stress on the colonic mucosa of the rat was investigated at various time intervals, ranging from one day to eight weeks. The amount of DNA synthesized by the mucosa was used as a marker of time-related events. A total of 75 Sprague-Dawley rats were investigated. Acute stress was considered for rats briefly plunged (psychic stimulus) or swimming for two hours (physical stimulus). Chronic stress was determined when rats were briefly plunged or swam for two hours for periods ranging from one to eight weeks. "Sham-transported" rats were used as controls. DNA in the descending colon decreased significantly in rats swimming for two weeks, but increased (even for plunged rats) at four and eight weeks. In the ascending colon, a substantial increase in DNA content was found in rats plunged or swimming for eight weeks. The descending colon appears to be quantitatively more affected by various stressors than the ascending colon. It is apparent that, in control rats, the mucosa of the descending colon differs from the ascending colon. Fluctuations in the colonic DNA synthesis throughout the experiment suggest that this phenomenon may be connected to compensatory mechanisms toward cell adaptation to stress conditions. The model may prove of value in studies of the therapeutic abrogation of the fluctuations of the DNA replication of the colonic mucosa during the acute and chronic phases of a given stress.