The purpose of this study was to compare urinary fluoride excretion with fluoride ingestion in children who had either a low fluoride intake or received supplemental fluoride through salt or water. The urinary samples were collected in two ways. In procedure A, urine was collected in the morning, at noon and during the afternoon. This covered a continuous period of approximately 7 h from the beginning to the end of the school day. In procedure B, morning, afternoon and night samples were collected. The morning and afternoon samples were obtained under supervision at school. Procedure B was more useful than procedure A for monitoring salt fluoridation projects. Children with a history of low fluoride intake excreted a mean of 10 μg F/h during the night and the morning, but 13–16 μg F/h after the main meal. Children in a water-fluoridated town or in comprehensive salt fluoridation programs excreted between 19 and 33 μg F/h. However, after the intake of meals prepared with fluoridated salt (250 ppm F) the mean excretion of fluoride ranged between 31 and 49 μg F/h. The levels of excretion corresponded with the levels of fluoride intake and meal patterns in the various g