The accumulation of Sr-90 in decayed or exfoliated human teeth was investigated by ultra low level beta counting. Fuming nitric acid and the necessary carriers and reagents were used for dissolving the samples, and the separation and purification of Sr-90. The Ca contents of samples were determined by flame atomic absorption spectrometry with Zeeman-effect background correction. A mixture of K and La used as a matrix modifier was found to be preferable for the determination of Ca in samples. The optimum concentration and concentration ratio of K and La on the absorbance of Ca in the NIST certified reference material, bone ash 1400 solution were determined. The reliability of the measurements was tested by analyzing Sr-90 in the IAEA certified reference material, animal bone, and Ca in bone ash 1400, by adding a K + La mixture. Recoveries are greater than 95% and relative standard deviations are lower than 10%. The detection limits of Sr-90 and Ca are 0.9 Bq/kg sample and 12.3 mug/L, respectively.