[(123)I]ADAM [2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine (ADAM)] has recently been shown to be a very promising imaging ligand for the detection of serotonin transporters (SERT) in human brain, because of its high specificity for SERT. [(123)I]ADAM has previously been used only for animal studies. In this work, we investigated the radiation dosimetry and biodistribution of [(123)I]ADAM based on whole-body scans in healthy human volunteers. Following the administration of 196+/-20 MBq (range 157-220 MBq) [(123)I]ADAM, serial whole-body images were performed up to 24 h. Estimates of radiation absorbed dose were calculated using the MIRDOSE 3.0 program with a dynamic bladder model. Twelve source organs were considered in estimating absorbed radiation doses for organs of the body. The highest absorbed organ doses were found to the lower large intestine wall (8.3.10(-2) mGy/MBq), kidneys (5.2.10(-2) mGy/MBq), urinary bladder wall (4.9.10(-2) mGy/MBq) and thyroid (4.3.10(-2) mGy/MBq). The effective dose was estimated to be 2.2.10(-2) mSv/MBq. The results suggest that [(123)I]ADAM is of potential value as a tracer for single-photon emission tomography imaging of serotonin receptors in humans, with acceptable dosimetry and high brain uptake.