Dentifrices containing fluoride and monofluorophosphate are possible sources of intake of fluorine compounds by humans, particularly young children. The purpose of the present study was to find the amount of monofluorophosphate toothpaste swallowed by children, utilizing the urinary excretion of fluoride as a marker, and to determine the fate of ingested monofluorophosphate. One hundred and five preschool children in Edinburgh, an area of low natural fluoride, were given a placebo paste to use for a week. A monofluorophosphate paste was then used for two weeks followed by a return to the placebo paste for a further week. Two 24-hour urine samples were collected from each child during each of the four weeks. The amounts of fluoride excreted were related to intake by determining the excreted proportion of a known dose. On average only 20 % of the fluorine was excreted in the urine. Ninety percent of the children swallowed less than 0.5 g of paste per day and only 7% of the children swallowed between 1 g and 2 g on any of the sampled days. This did not occur regularly with any of the children.