[en] This Co-ordinated Research Project (CRP) addresses an important public health issue in many developing areas, which is the existence of high rates of infection and diarrhoea disease and its deleterious effects on the health and nutritional status of infants and children around the world. Persistent diarrhoea with associated malnutrition remains a major cause of morbidity and mortality in the developing countries. There are established relations between diarrhoea disease and Helicobacter pylori infection and the latter may also additionally specifically impair nutrient absorption. Helicobacter pylori infection is likely to be the most common world wide bacterial infection, and it is estimated that approximately 50% of the general population is affected. The World Health Organisation has classified H. pylori as a Group 1 carcinogen. Young children in developing countries are the main targets of infection, with a substantial risk of developing gastric carcinoma during adulthood. High infection rates of H. pylori among new-borns and young children in developing nations appear to be a major cause for chronic under-nutrition and diarrhoea syndrome with failure to thrive. This bacterium can survive in the acidic interior of the human stomach due to its capacity to secrete an enzyme called urease, which decomposes the urea contained in the stomach's interior into ammonia and carbon dioxide increasing the pH move underneath the protective mucous membrane in the stomach where it is protected from the caustic stomach acid. This transitory drop in stomach acidity, explained by a diminished gastric secretion and an increase in ammonia production during infection, promotes the transit of lower bowel pathogens leading to repeated gastrointestinal infections, causing diarrhoea and adverse consequences on nutrition and growth. This CRP seeks to identify and assist research groups in developing countries, which plan to conduct studies on the area of H. pylori infection and its impact on nutrient assimilation, nutritional status and growth, using ¹³C labelled substrate breath tests, and other isotopic techniques. The specific research objectives are the following: To quantify the magnitude of the prevalence of H. pylori infection in different developing areas by using the ¹³C urea breath test; To study carbohydrate, fat and protein assimilation, that is digestion, absorption or metabolism of these macronutrients, by using ¹³C labelled substrates breath tests; To assess nutritional status, i.e., growth and body composition by anthropometric techniques, and specific micronutrient deficiencies; To gain further information on the onset of H. pylori in infants and children by identifying modes of transmission, specific risk factors, and to learn more on the demographic, socioeconomic and hygienic conditions in developing areas; To study possible association between H. pylori (H.p.) infection and its socio-economic risk factors with diarrhoea morbidity and nutritional status in developing areas. The purpose of this first Research Co-ordination Meeting (RCM) was to discuss and establish basic protocols of ¹³C breath tests for sample collection and analysis