This report summarizes the present state of knowledge in dosimetry of the Hiroshima-Nagasaki A-bomb survivors. Data have been presented on the physical factors involved in the two cities and on attenuation of radiation by various shielding situations. This information is being used to estimate a tentative radiation dose to individual A-bomb survivors. It should be emphasized that many important problems remain to be solved before accurate doses can be assigned to individual survivors. Such information will greatly strengthen investigation of biological consequences of instantaneous doses of gamma and neutron irradiation in men. 18 references, 9 figures.