We examined the effects of chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA) on fasting motility patterns and transit in ileocolonic loops of 5 dogs. Animals were prepared with isolated loops (40 cm ileum and 5 cm colon) which maintained neuromuscular continuity with the intact bowel through a bridge of tunica muscularis. Myoelectrical activity was recorded from multiple serosal, monopolar electrodes and muscle contractions recorded from serosal strain gauges; fluid transit was assessed by continuous perfusion (1.4 ml min-1) of solutions containing polyethylene glycol 4000 marker, with or without bile acids. Saline perfusion did not disturb the fasting cycle of motility and mean cycle length in unperfused (106 +/- 7 min) loop was the same as during perfusion of saline (108 +/- 9 min). Bile acids abolished interdigestive cycles in 11 of 12 experiments, fasting patterns returned 64-106 min after bile acid perfusion was stopped. The fasting pattern continued to cycle normally in the proximal small bowel during bile acid perfusion. CDCA (15 mM) stimulated the occurrence of propulsive contractions of long duration. Bile acids shortened transit time through the loops and altered the pattern of flow towards a more continuous, steady stream. These effects of bile acids on ileal motility, like those described previously in the colon, could play a role in bile acid diarrhea.