1. Cholic, taurocholic and dehydrocholic acids were administered I.V. to rats, rabbits and dogs (3·12-100 mg/kg). With the higher doses of cholic acid, the bile flow was increased sixfold in the dog and only 2 to 2½-fold in the rat and rabbit. The choleretic response was also maintained for a longer time in the dog (90 min) than in the rat or rabbit (20-30 min).