Twenty-five premolars (from Nagoya, Japan < 0.1 parts/10(-6)F in drinking water) were sampled to determine the fluoride content in imbrication lines of Retzius between the grooves and ridges of perikymata on the enamel surface. Eight small windows were formed on each surface in groove and ridge regions using an etched microsampling technique. By using a regression curve, y = ax(-b), fluoride concentrations were compared at depths of 1, 3, 5, 10, 20, 30 and 50 microm in the perikymata regions. Fluoride concentrations increased gradually from the age of 10 to 12 years on the premolar surfaces, but were significantly higher in 12-year-olds or older (erupted teeth) than in 10-year-olds or younger (unerupted teeth). No obvious difference in fluoride concentrations was found between males and females. In the outermost enamel ( < 5 microm depth), fluoride concentrations were significantly higher in the grooves than the ridges of the perikymata. Comparison of the exponential regression coefficients (-b) of the fluoride profiles showed a significant difference between the grooves and ridges. It was concluded that fluoride concentrations and profiles were higher in grooves than in ridges of perikymata, probably because they are naturally porous and are stagnation areas attracting dental plaque.