A prospective, placebo controlled, triple blind clinical trial was undertaken in Thailand to determine the effect of Lactobacillus GG on recovery from acute diarrhoea in children. Thirty-nine children (mean age=8 months) were enrolled and following rehydration received either oral Lactobacillus GG (n=20) as a freeze-dried preparation or placebo (n=19) twice daily for 2 days. The clinical characteristics of the study groups were similar. There was no significant difference overall in clinical response detected between the study groups. When only those with acute non-bloody diarrhoea (n=26) were considered, the mean duration of diarrhoea was significantly shorter in the lactobacillus group (1.9 days) than in the placebo group (3.3 days) (P<0.055). Stool frequency was less on the second day in the lactobacillus group (P<0.05). The results suggest thatLactobacillus GG accelerates recovery from acute watery diarrhoea in young children in a tropical setting.