Physical characteristics of a dose calibrator CRC-30BC (Capintec, Mt. Vernon, N.Y.) was studied in the present study. We performed repeated measurements of the radioactive sample, changing its position in the well, its volume, and its radioactivity. In terms of the vertical dependence, the highest activity was obtained 7-8 cm from the bottom of the well. For axial dependence, the lowest activity was obtained at the center of the well. The sample volume, which ranged from 1 ml to 4 ml, did not have a substantial effect on the reading of the radioactivity. As long as the center of the sample remained positioned at the appropriate point in the well, the calibrator responded proportionally to the true radioactivity, which ranged from 4.625 MBq (0.125 mCi) to 592 MBq (16 mCi). The radioactive value on the dose calibrator was reliable enough to employ in quantitative evaluation when attention was paid to the position of the radioactive source.