The goals of this project were to determine the minimal infectious dose and medical significance of an enteric virus ingested in drinking water. The study was conducted under double-blind, placebo-controlled, random-selection conditions. A total of 149 susceptible (antibody-free), healthy, young adult males ingested varying doses of ECHO-12 virus (10-10,000 pfu) or placebo seeded into 100 ml of non-chlorinated water and were followed for evidence of illness, viral shedding, and antibody response. There was no illness in any of the subjects and no evidence for infection among the placebo subjects. Infection in exposed subjects was primarily demonstrated by fecal shedding of virus.