In an effort to elucidate whether bacteremia occurs during endoscopic examination of the lower gastrointestinal tract, two prospective studies were undertaken involving patients undergoing colonoscopy and proctosigmoidoscopy. The former group has been presented earlier, and the second study, which includes the proctosigmoidoscopy group, is the basis for this study. Fifty-seven patients undergoing proctosigmoidoscopy were studied. Excluded from the study were patients with fever, diarrhea, inflammatory bowel disease, valvular heart disease, vascular prosthesis, chemotherapy, and immunosuppression. Aerobic and anaerobic blood cultures were taken before, during, and after proctosigmoidoscopy. Additional cultures were taken after a biopsy or polypectomy. Skin cultures were taken from the venipuncture site prior to venipuncture. No bacteremia was demonstrated. Three blood cultures were positive, but all were considered contaminants on the basis of the nature of organisms. No correlates could be drawn as to the depth of insertion, length of time, or position of patient during the procedure. It is concluded that no significant bacteremia occurs during proctosigmoidoscopy. Further studies are warranted in the excluded high-risk group.