This study examines the role of different types of small intestinal distention of affective behavior. "Isovolemic" and volumetric distention were hypothesized to have different effects in rats. Both stimuli decreased fluid consumption in a free drinking situation equally. Behavioral correlates, however, were clearly different. Changes of the gut volume were accompanied by behavioral elements characteristic to aversivity while such changes were not observed when the distention was isovolemic. These results indicate that the cessation of intake, i.e., satiety, is not the consequence of the interference of concurrent aversive behavior. In contrast with these findings, isovolemic distention proved to be mildly unpleasant when tested by the taste-aversion method, although the effect was clearly distinct from that of volume changes. The results suggest that not avrsivity but discomfort may be a steady, inherent concomitant factor of physiological mechanoceptive gut stimuli.