Microdosimetric calculations of Re-186 and Re-188 have been evaluated at the cellular level. Stopping power, LET, range values and deposited energies per decay have been calculated for beta particles, Auger and conversion electrons. In addition, total absorbed doses have been calculated for the radionuclides distributed randomly with certain activities within the cell. Results indicate Re-186 and Re-188 to be promising radionuclides for therapy of tumors from millimeter through centimeter dimensions. (c) 2004 Elsevier Ltd. All rights reserved.