Background:Certain strains of lactobacilli may promote recovery from acute diarrhea.Lactobacillus reuteriis of human origin and is a natural colonizer of gastrointestinal tract. In this trial, exogenously administeredL. reuteriwas studied as a therapeutic agent in acute diarrhea.Methods:Forty patients between 6 and 36 months of age hospitalized with acute diarrhea (75% rotavirus) were studied. After parental consent, the patients were randomized to one of two treatment groups to receive either 1010to 1011colony-forming units ofL. reuterior a matching placebo daily for the length of hospitalization or up to 5 days. The clinical outcome of diarrhea and colonization ofL. reuteriwere evaluated.Results:The mean (SD) duration of watery diarrhea after treatment was 1.7 (1.6) days in theL. reuterigroup and 2.9 (2.3) days in the placebo group (p = 0.07). On the second day of treatment only 26% of patients receivingL. reuterihad watery diarrhea, compared with 81% of those receving placebo (p = 0.0005). Cultures of lactobacilli from stool samples demonstrated that administration ofL. reuteriresulted in colonization of the gastrointestinal tract.Lactobacillus reuteriaccounted for >75% of the total lactobacilli found in children fed with this product.Conclusions:Lactobacillus reuteriis effective as a therapeutic agent in acute rotavirus diarrhea in children. Further studies are warranted to confirm the present finding and to explore the full therapeutic potential ofL. reuteriin acute viral diarrhea.