Normal human kidney, lung, liver, heart, skin, thymus, spleen, lymph node, pancreas, and choroid plexus were reacted with a C3b-coated particle (fluoresceinated Salmonella typhi) to determine if these tissues contained C3b receptor cells. Clusters of these cells were identified in the spleen, lymph nodes, and in the renal glomeruli. All other studied tissues demonstrated a minimal homogeneous deposition of the indicator bacteria throughout the entire aspect of the tissue. Deposition of the indicator bacteria on the tissues was abrogated when the bacteria were prepared with heat inactivated serum as a source of complement.