We evaluated the effect of Saccharomyces boulardii administration in otherwise healthy children aged between 6 months and 10 years who were admitted for acute diarrhoea (15 males, 12 females). The patients were randomized into two groups: group 1 (n = 16) received 250 mg S. boulardii dissolved in 5 ml of water orally twice daily for 7 days and group 2 (n = 11) received placebo. Clinical and laboratory assessments were performed on admission and on day 7 of follow-up. Both groups experienced reduced daily stool frequency, the decrease being significantly greater in group 1 on days 3 and 4 compared with group 2. Group 1 demonstrated significant increases in serum immunoglobulin A and decreases in C-reactive protein levels on day 7. The percentage of CD8 lymphocytes on day 7 was significantly higher in group 1 than group 2. This study confirmed the efficacy of S. boulardii in paediatric acute gastroenteritis and the findings suggest that S. boulardii treatment enhances the immune response.