Lactobacillemia is rare and, to our knowledge, previously undescribed in liver transplant patients. We reviewed the clinical records of all patients who had undergone orthotopic liver transplantation between January 1985 and August 1992 for whom a blood culture after transplantation yielded Lactobacillus species. A case-control study for determination of risk factors for lactobacillemia in this patient population was also performed. Eight cases of lactobacillus bacteremia were identified. All patients received nonabsorbable oral antibiotics for selective bowel decontamination. In addition, six of eight case patients received intravenous vancomycin prior to the development of lactobacillemia. The biliary anastomosis in each case patient was a Roux-en-Y choledochojejunostomy. Analysis of the case-control study revealed that the presence of a Roux-en-Y choledochojejunostomy at the time of lactobacillemia is a statistically significant risk factor (odds ratio [OR] = infinity, 95% confidence interval [CI] = 1.8-infinity, P < or = .05) but that prior administration of intravenous vancomycin is not a statistically significant risk factor (OR = 2.6, 95% CI = 0.38-30.0, P value not significant) for lactobacillemia. The use of selective bowel decontamination and of intravenous vancomycin in liver transplant patients may select for Lactobacillus species. Furthermore, a Roux-en-Y choledochojejunostomy may allow colonization of the intrahepatic biliary tract with enteric flora.