Selected probiotics (mainly Lactobacilli, and particularly LGG, and Saccharomyces boulardii) have recently demonstrated a therapeutic efficacy in acute diarrhoea, if used in the early phase of infection and at high concentration. Further data are needed to clarify their effect for prevention and travellers' diarrhoea. The mechanisms of action of probiotics need to be fully elucidated but seem to include a complex interaction of epithelial, molecular, metabolic and immune responses. There is an increasing evidence that different micro-organisms show different properties and efficacy. An accurate identification and selection of the strains, the dose and the patients are thus crucial for a correct therapeutic approach. Prebiotics can modify the intestinal flora and interact with the immune system of the host against specific pathogens. However, clinical trials are currently limited and a beneficial effect of prebiotics in acute diarrhoea is still lacking. In developing countries zinc supplementation demonstrated a significant reduction of fecal excretion, duration, severity and persistency of diarrhoea. Moreover, zinc may improve immune status, intestinal permeability, epithelial and enzymatic functions, and transport of electrolytes. The use of zinc in addition to oral rehydration solution (ORS) could thus theoretically improve the treatment and reduce the complications of diarrhoea worldwide. However, in developed countries, no trial using zinc supplementation in patients with acute diarrhoea has been published yet and the cost-benefit ratio of zinc supplementation needs to be assessed.