BACKGROUND Fecal pellet output has been assessed as a colonic motor activity because of its simplicity. However, it remains unclear whether an acceleration of colonic transit correlates well with an increase in fecal pellet output. We examined the causal relationship between colonic transit and fecal pellet output stimulated by the central application of corticotropin-releasing factor (CRF) and restraint stress. METHODS Immediately after intracisternal injection of CRF, (51)Cr was injected via a catheter positioned in the proximal colon. Ninety minutes after (51)Cr injection, the total number of excreted feces was counted, and then the rats were killed. The radioactivity of each colonic segment was evaluated, and the geometric center (GC) of the distribution of (51)Cr was calculated. For the restraint stress study, after administration of (51)Cr into the proximal colon, rats were submitted to wrapping restraint stress for 90 min. Then they were killed, and GC was calculated. RESULTS Both restraint stress and CRF significantly accelerated colonic transit. There was a positive correlation observed between fecal pellet output and GC of colonic transit in response to restraint stress, but not CRF, when the number of excreted feces was more than three. In contrast, there was no significant correlation observed between the two in stress and CRF when the number of excreted feces was less than two. CONCLUSIONS The acceleration of colonic transit in response to restraint stress and central administration of CRF does not always correlate with an increase in fecal pellet output.