Infectious gastroenteritis continues to be a leading cause of mortality and morbidity worldwide. The cornerstone of treatment remains replacement of water and electrolyte losses with oral rehydration solution. Until a few years ago, probiotics were discussed primarily in the context of alternative medicine, but they are now entering mainstream medical practice since a decrease of the severity and duration of infectious gastroenteritis in approximately 24 hours has been shown for some strains. Therefore, probiotics are a potential add-on therapy in acute gastro-enteritis. The shortening of the duration of diarrhoea and the reduction in hospital stay result in a social and economic benefit. Evidence found in viral gastroenteritis is more convincing than in bacterial or parasitic infection. Mechanisms of action are strain specific and only those commercial products for which there is evidence of clinical efficacy should be recommended. Timing of administration is also of importance. In acute gastroenteritis, there is evidence for efficacy of some strains of lactobacilli (e.g. Lactobacillus caseii GG and Lactobacillus reuteri) and for Saccharomyces boulardii. Probiotics are "generally regarded as safe", but side effects such as septicaemia and fungaemia have very rarely been reported in high-risk situations. Although most studies conclude in a statistically significant shortening of the duration of diarrhea, the clinical relevance of this finding is limited. In conclusion, selected strains of probiotics result in a statistically significant but clinically moderate benefit in shortening the duration of diarrhoea caused by acute infectious gastroenteritis.