Lower extremity vascularity in nine patients with sickle cell anemia was studied by intra-arterial Tc-99m human albumin microspheres or intravenous thallium 201. In eight patients, the normal pattern of greater muscle than bone activity was reversed with marked tracer localization in skeletal parts usually not visualized. In four cases, there were distinct focal abnormalities in the femurs and tibias which correlated with defects on Tc-99m sulfur colloid marrow scans. Tc-99m pyrophosphate bone scans demonstrated normal uptake in the same areas. The scintigraphic findings indicate a markedly increased relative bone marrow blood flow.