Tonga, like many developing countries, suffers from a shortage of medical staff and a high morbidity and mortality from paediatric diarrhoeal disease. In 1980 a programme was started to train medical assistants and village administrators in the correct use of oral rehydration salt solution for rehydration. The effect on morbidity, mortality, and admission to hospital over the six years 1978-83 was assessed. After the introduction of the scheme the number of deaths due to diarrhoea fell considerably and the state of hydration in children admitted to hospital with diarrhoea greatly improved. It is recommended that similar programmes be adopted where clinical problems of diarrhoea with dehydration persist. Instruction in the use of oral rehydration fluid was most effectively given by non-medical staff to groups of mothers, rather than by paediatricians in their inevitably brief, although important, explanation given in hospital.