To study the interaction between diarrhoea and malnutrition, an average of 300 children aged 5-24 months were followed from January 1981 to January 1983 in Teknaf, Bangladesh. Diarrhoea episodes, differentiated according to stool appearance, were recorded weekly while weight and height measurements were taken every 6 months. Results showed no relationship between the nutritional indicators and diarrhoea incidence recorded within 60 d after anthropometric assessment. However, the duration of dysentery was significantly longer in the severely malnourished children who were stunted but not for those wasted. Although many children with watery diarrhoea had episodes of long duration, these were not associated with any nutritional indicator. We conclude that the key factors in this interaction are the invasive type of pathogen and chronic malnutrition.