1. A comparative study of the iodine and calcium contents of diets in areas of Ceylon where goitre is endemic and non-endemic was carried out.
2. The iodine content of food grown in non-endemic areas was, in most instances, considerably higher than in endemic areas.
3. In endemic areas the daily average intake per person per day was well above the allowance of 100–150 μg recommended by most workers. The critical level of total daily iodine intake below which goitre becomes endemic in Ceylon was 400 μg. Possible reasons for this higher need of iodine are discussed.
4. Addition of iodine to cooking salt has been used successfully to combat endemic goitre in many countries. The amount of iodine added is based on the degree of endemicity and the amount of salt consumed per person per day. It is suggested that the more important criteria which should determine the amount of iodine added to cooking salt are the dietary iodine content, the daily total intake of dietary iodine and particularly the level of iodine below which goitre becomes prevalent.