Radionuclide separation and preconcentration methods were developed for two types of biological samples that play a role in assessing internal radiation contamination. For the determination of Pu-238 in urine, either as a single isotope or in a mixture, a dispersive liquid-liquid microextraction technique was used for extraction. Parameters including dispersers, extractants, back extractants and pH were optimized to achieve high recoveries of plutonium. Liquid scintillation counting was used for samples containing only plutonium, and alpha spectroscopy was used for samples containing a mixture of isotopes. For the determination of Am-241 in a humerus from a deceased worker exposed to americium 40 years prior, subsamples were taken by shaving successive layers off the bone (from the periosteum to the marrow) for dry/wet ashing before americium was isolated by extraction chromatography and determined using alpha spectrometry. The results showed americium retention and migration throughout the total bone volume.