b A meihod which provides boih a permanent visual record, and a quantitative estimation of inorganic fluoride in the range of 1 to 1 0 pg. is described.The fluoride is precipitated onto a filter paper disk as CI calcium fluoride complex containing thorium ions. After suitable elution procedures the thoriumfluoride complex is stained with solochrome brilliant blue and then extracted from the paper. The absorbance of the solution is read at a wavelength of 600 mp.