The incorporation of naturally occurring thorium isotopes in human femur bones was studied by analyzing 28 bone samples. The results show that the activity concentrations of Th-232 and Th-230 are in the range of the blank values resulting in an upper limit of theirs activity concentrations in human bones. The presence of Th-228 can be attributed, on the basis of model calculations, to the radioactive decay of deposited Ra-228. We conclude that thorium is not detectably incorporated into human bones.