[en] Laser excitation produces highly excited atoms which are efficiently ionized by collisions with an inert buffer gas. This effect, resonantly enhanced collisional ionization (RECI), is being developed as a means of measuring radionuclides of interest to internal dosimetry; specifically, uranium and transuranic species. Initial proof-of-principle experiments have given femtogram detection limits for calcium. Recently, RECI signals have been observed from uranium and detection limits in the same range are anticipated. For the transuranics, where isotope shifts are large, modest laser bandwidths of /approximately/0.1 cm/sup /minus/1/ can provide isotopic selectivity in the excitation process. 4 refs., 2 figs