The efficacy of probiotics on persistent diarrhea remains uncertain. The purpose of this study was to evaluate the effect of Lactobacillus sp and Saccharomyces boulardii on persistent diarrhea in children. In a double-blind trial eighty-nine children, aged 6-24 months were randomly distributed to receive pasteurized cow milk containing 2 viable lyophilized strains Lactobacillus casei and Lactobacillus acidophillus strains CERELA, (10(10)-10(12) colony-forming units per g) (n = 30), or lyophilized S. boulardii, (10(10)-10(12) colony forming units per g) (n = 30) or pasteurized cow milk as placebo (n = 29); on each diet 175 g was given twice a day for a 5 day period. Number of depositions, duration of illness and frequency of vomiting were considered. Enteric pathogens were isolated from stools in 40% of the patients, 27% had rotavirus. Lactobacillus and S. boulardii significantly reduced the number of depositions (p < 0.001) and diarrheal duration (p < 0.005). Similarly both significantly (p < 0.002) reduced vomiting as compared with placebo. There was no difference between treatments depending on rotavirus status. In conclusion, L. casei and L. acidophillus strains CERELA and S. boulardii are useful in the management of persistent diarrhea in children.