The aim of this study was to determine organ uptake and dosimetry in human subjects using 111In granulocytes obtained by ficoll-hypaque purification. Anterior-posterior whole-body imaging was performed at 1, 3, 5, 24 and 48 h after injection of approximately 18.5 MBq (0.5 mCi) 111In granulocytes in 10 normal volunteers. Utilizing relative geometric mean analysis, the fraction of injected activity (FIA) was determined at each imaging time for the kidney, liver, lungs, bone marrow, spleen and whole-body remainder. Residence time was determined by integration of the bi-exponential fit of the FIA data over time. Curve fitting was performed with SAAM software (University of Washington). Red marrow uptake was calculated from activity in the L3-L4 vertebrae and iliac crests. Total body marrow uptake was extrapolated from these data using ICRP 23. Dose was determined with MIRDOSE 2 for the various organs. The liver had the highest organ uptake (40.3% at 48 h). The spleen, liver, red marrow, kidney and lung doses were 4.1, 1.6, 0.8, 0.5 and 0.4 mGy MBq-1, respectively. Urinary and stool excretion was negligible and blood clearance half-time was 6.9 h. Using current methods providing improved quantification of organ uptake and dosimetry, our results confirm the liver, spleen, bone marrow,lungs and kidneys to be the principal target organs of 111In granulocytes.