Bladder and brain time-activity measurements in humans were performed after the intravenous administration of 2-[F-18]fluoro-2-deoxy-D-glucose. Radiation doses were calculated using the MIRD schema. The bladder wall received an average of 440 mrad/mCi (s.e. 76) in ten subjects who voided at 2 hr after administration of tracer. If these subjects had voided at 1 hr, the bladder-wall dose would have been reduced to 220 mrad/mCi. The brain received an average of 81 mrad/mCi in eight subjects. The doses to other organs, calculated from published dog biodistribution data, are between 50 and 85 mrad/mCi except for spleen and heart, which both received 160 mrad/mCi. These time-activity measurements for the critical organ in the human avoid the assumptions made in using animal biodistribution data for human dosimetry calculations.