We set out to establish an appropriate and convenient method for calculating alpha-particle absorbed doses to the liver and spleen of Thorotrast patients and to estimate a representative dose rate to the liver for the whole population of surviving and deceased Thorotrast patients in Japan. First, we determined steady-state activity ratios of 232Th progeny from 13 autopsy cases and found them to be identical to those reported in German subjects. Second, we estimated the alpha dose rates in 206 subjects at autopsy from radioactivity measurements and terminal weights of the organs. Combining these results with measurements of exhaled 220Rn in survivors, we considered the representative dose rates at injection to be 0.22 Gy y−1. Additionally, our data suggest that deposition in the spleen has previously been overestimated. This is an error with some bearing on the evaluation of leukemia risks from alpha-particle irradiation.