The aim of this study was to determine what weaning foods and food preparation practices expose children to a high risk of diarrhoeal disease through exposure to a contaminated diet. Bacterial contamination of 897 food and 896 drinking water samples was assessed in a water and sanitation intervention project. The geometric mean of faecal coliforms per g or ml was 7.5 x 10(3) in left-over rice. 1.4 x 10(2) in other types of boiled rice, 2.5 x 10(2) in milk, 4.8 in household drinking water, and 3.5 in bread. Multiplication of faecal coliforms occurred when there was a delay of more than 4 h between preparation and consumption of food. All samples were more contaminated in the rainy than in the dry season. Strategies to reduce contamination should therefore focus on 'wet' foods, early consumption after preparation, and re-heating of left-over foods. Understanding the reasons for the faulty practices is also essential to the formulation of effective measures.