 Subjects susceptible to the human norovirus GII.4 challenge strain, CIN-1 i.e. presence of a functional FUT-2 gene, regardless of ABO blood type, will be housed in the Cincinnati Center for Clinical Research CCCR inpatient facility and challenged orally with different doses of the virus. The challenge study will be conducted in 2-3 cohorts of approximately 20 subjects each, with the initial cohort receiving 103 RT-PCR units or placebo 9 challenge and 1 placebo per 10 subjects. Based on the illness rate of acute gastroenteritis AGE in the initial cohort, the second cohort will be enrolled to receive a challenge dose based on the results of the previous studies. Additional cohorts may be necessary. Illness is defined as infection accompanied by vomiting andor diarrhea during the inpatient stay.Two to three additional subjects per cohort will serve as alternates in the event that any of the study subjects are unavailable or become ineligible at the time of the inpatient study.Subjects will remain in the inpatient facility for at least four days following challenge and assessed daily for clinical and virologic evidence of norovirus infection. Subjects will return to the investigational site for evaluation on Day 6 6-8 days and about 15 14-16 days and 30 days 28-35 days, and 45 40-45 days, and 55-65 post challenge. 