Background:Oral administration of liveLactobacillus caseistrainGGis associated with the reduction of duration of diarrhea in children admitted to the hospital because of diarrhea. The purposes of this work were to investigate the clinical efficacy of oral administration ofLactobacillusin children with mild diarrhea who were observed as outpatients, and to see whetherLactobacillus GGcan reduce the duration of rotavirus excretion.Methods:Duration of diarrhea was recorded in 100 children seen by family pediatricians and randomly assigned to receive oral rehydration or oral rehydration followed by the administration of lyophilizedLactobacillus casei,strainGG. Rotavirus was looked for in the stools of all children and, in those in whom results were positive, stools were examined again 6 days after the onset of diarrhea.Results:In 61 children results were positive for rotavirus and in 39 results were negative. Duration of diarrhea was reduced from 6 to 3 days in children receivingLactobacillus GG,with a similar pattern in rotavirus-positive and -negative children. Six days after the onset of diarrhea, stools in only 4 out of 31 children that receivedLactobacillus GGwere positive for rotavirus compared with positive findings in 25 out of 30 control subjects.Conclusions:Oral administration ofLactobacillus GGis effective in rotavirus-positive and rotavirus-negative ambulatory children with diarrhea. Furthermore, it reduces the duration of rotavirus excretion.