Objective : A double-blind randomized controlled-trial was done to evaluate the efficacy of tyndalizedLactobacillus acidophilus in acute diarrhea.Methods : All children from 6 months to 12 years with acute diarrhea were included.Lactobacillus acidophilus/placebo was given to the children for 3 days with ORS and feeds. Intake-output was recorded 4 hourly. Of the 98 children, 48 receivedlactobacillus and 50 the placebo.Results : ORS consumed, frequency of stools, duration of diarrhea, time for rehydration, hospital stay, weight gain and IVF needed were comparable in the two study groups. There were 4 treatment failures in thelactobacillus group and none in the placebo group (OR 0.92,95%CI 0.84–0.99). In the rotaviral diarrhea and in those who had diarrhea of less then 60 hours the difference did not reach statistical significance.Conclusion : There is no significant benefit of tyndalizedLactobacillus acidophilus in acute diarrhea.