[en] This report addresses the possible use of Sputter-Initiated Resonance Ionization Spectroscopy for analysis of uranium, plutonium and thorium in urine (principally), blood and feces. The method appears capable of performing such analyses on urine down to levels of 0.05 microgram uranium per liter or lower at reasonable cost and with good accuracy. A preliminary chemical separation would be required, as with most other methods. Anion exchange from strong HCl solution appears highly satisfactory for the separation. No method capable of distinguishing between isotopes of the same element can be employed without chemical pretreatment that is at least as extensive. The experimental steps necessary to verify these conclusions are indicated