The fluoride concentration in drinking water and in urine of the inhabitants of 94 localities in Northern and Central Poland was determined. The analyses were performed potentiometrically using a fluoride-specific electrode. In most of the localities the fluoride concentration in water was < 0.3 mg/l, which is far below the recommended level for caries control. In these communities fluoridation of water is advised. In six localities the water fluoride concentration was 1.2 mg/l. The elevated water fluoride is of natural (Malbork) as well as of anthropogenic (Wiślinka) origin. The mean fluoride level in the urine in the investigated localities was 1.10 mg/l (range 0.10-2.67 mg/l). No significant correlation between the concentration of fluoride in drinking water and human urine was found in this study. This suggests that the elevated fluoride level in urine may be caused not only by the water fluoride, but also by the inhalation of dust particles containing fluoride, and by the diet.