OBJECTIVE To determine fluoride excretion under various conditions of fluoride intake and to estimate the fractional urinary excretion of fluoride in individual children participating in a school milk fluoridation scheme. METHODS In the first part of the study, individual urine samples were collected from each of eight 4 to 5-year-old children for a continuous period of 55 h. For each child (n = 8) and for each day (n = 3) the maximum urinary fluoride concentration (p.p.m.F), the maximum fluoride excretion rate (microgram F/h) and the total daily fluoride excretion (mg) were calculated. The second part of the study was carried out to determine the 24 h fractional percentage of fluoride excreted following administration of a known dose of fluoride in the absence of other sources. RESULTS Under usual conditions of fluoride intake (i.e. milk containing 0.5 mg fluoride, customary diet and toothbrushing with fluoride toothpaste) the children's daily fluoride excretion was 0.33 mg. The fractional urinary fluoride excretion of a 0.5-mg fluoride tablet was 30%. CONCLUSIONS It is concluded that the children's mean 24 h fluoride excretion was somewhere between that reported in low fluoride conditions and that reported in optimally fluoridated areas. The fractional urinary fluoride excretion was found to be in agreement with the findings of other workers.