Female New Zealand White rabbits, following sham laparotomy, total splenectomy and splenectomy with 50% splenic autotransplantation, have been injected intravenously with 99Tc-labelled type 2 Streptococcus pneumoniae. The blood clearance of isotope has been measured and the numbers of circulating bacteria quantitated by blood culture. On sacrifice of the animals the tissue uptake of the isotope has been measured. The results indicate 98% bacterial clearance from the blood within 7 min. The liver is the principal organ for reticuloendothelial uptake of the bacteria accounting for 60% of the total injected dose; 15% of the isotope clearance occurred in the lungs, and the spleen contributed only 3% of the total bacterial clearance. There was no difference in the observed pattern of clearance following splenectomy and following splenic reimplantation. Following the uptake of the bacteria in the tissues, the isotope dissociated from the bacterium and was excreted in the urine. The secondary rise in blood isotope level consequent upon this release was not accompanied by a secondary bacteraemia.