A group of 175 patients had barium enema. Pour-plate blood cultures were obtained immediately before and after the procedure and 5, 10, 15, and 30 minutes later. Bacteremia was demonstrable in 20 (11.4%) patients. In some, blood cultures were positive for as long as 15 minutes after barium enema; all were negative at 30 minutes. Among the bacteria associated with the 20 episodes of bacteremia were Escherichia coli, Klebsiella, enterococci, Proteus morganii, Bacteroides, and Veillonella. The incidence of bacteremia among patients with ulcerative colitis, regional enteritis, rectal polyps, colonic or rectal carcinoma, nonspecific diarrhea, or other lower intestinal tract disorders was not much different from patients free of rectosigmoid disease. The results of this study suggest that a history of recent barium enema may be important in patients who have endocarditis.