Orally administered bovine immunoglobulins with specific activity against colonization factors of enterotoxigenic Escherichia coli (ETEC) could provide passive protection against ETEC challenge in volunteers. Twenty healthy adult volunteers ingested either a placebo or a partially enteric-coated preparation of bovine immunoglobulins with activity against the colonization factor antigens CFA/I, CS3, and CS6 and then were challenged with ETEC strain E24377A (CS1+, CS3+) administered with a standard meal. There was no difference in the incidence or severity of diarrhea among the 10 volunteers who received the bovine immunoglobulins and the 10 who received placebo. Either the specificity or titer of anti-colonization factor antibodies or the formulation of antibodies in this product was not adequate to provide passive protection against ETEC challenge.