One hundred patients undergoing postoperative cholangiography had blood cultures drawn prior to and 15 minutes and six hours after cholangiography. Bile cultures obtained prior to cholangiography grew organisms in 92 of 100 patients with E. coli, Klebsiella pneumoniae and enterococcus being the bacteria most frequently isolated. Anaerobes were isolated from the bile in 21% of the patients. Nine of 83 patients (11%) not receiving antibiotics developed a bacteremia after cholangiography with organisms identical to those in the bile. All nine patients recovered without further complications of cholangiography. Those who developed a bactermia could not be distinguished from the group as a whole on the basis of age, sex, laboratory data, type of surgery or cholangiographic findings. None of the eight patients with negative bile cultures and none of 17 patients on antibiotics at the time of cholangiography experienced a bacteremia. Ninety to 93% of 304 organisms isolated from the bile were sensitive to a combination of a penicillin and an aminoglycoside. Most patients undergoing postoperative tube cholangiography do not develop a bacteremia and do not require antibiotics. Only patients with positive bile cultures who might tolerate a bacteremia poorly, and those who are febrile from cholangitis immediately prior to cholangiography should be covered with a short course of systemic antibiotics.