Salivary fluoride concentrations were investigated in 12-year-old children living in areas with low (0.1 ppm) or high (1.2 ppm) fluoride concentration in the drinking water. Unstimulated whole saliva was collected from 27 children from the respective areas every 2nd hour for 46 h except during sleep. The mean salivary fluoride concentration was 0.32 +/- 0.013 mumol/l (n = 419) in the low-fluoride (LF) area and 0.87 +/- 0.047 mumol/l (n = 401) in the high-fluoride (HF) area. No significant rhythm could be found for the diurnal variations in the mean or individual salivary fluoride concentrations. However, in the HF area the individual salivary fluoride concentrations fluctuated widely and randomly.