This study enrolled 60 healthy volunteers from four institutions (Johns Hopkins University, Pennsylvania State University, Memorial Health University Medical Center, and Temple University. Subjects had to be healthy men or women 18-65 years old with no gastrointestinal disease as confirmed by initial screening using a modified Mayo Clinic Research Gastrointestinal Disease Screening Questionnaire, and normal results for CBC, metabolic profile, serum amylase and gallbladder ultrasonography. Women could not be enrolled if pregnant.