Chronic, non-specific `toddler diarrhoea' in young children is often accompanied by an increase in plasma prostaglandins, particularly PGF2α. Although treatment with drugs is generally unnecessary, aspirin is effective in most children with high prostaglandins, and treatment with loperamide is effective in most children with toddler diarrhoea, regardless of the plasma prostaglandin levels. The source of the increased plasma prostaglandins is not known.