Nine patients with sickle cell disease (SCD) who were hospitalized at UC Davis Medical Center for vaso-occlusive crisis (VOC) were studied as part of a randomized double-blind phase III clinical trial to investigate the real-time effects of poloxamer 188 on VOC. All patients showed significant microvascular changes from normal (steady-state) values during VOC (diminished venular diameter and red cell velocity). The patients were randomly assigned to be treated with poloxamer 188 or placebo. Poloxamer 188 (n = 4) but not placebo (n = 5) significantly reversed these microvascular changes ˜ 2 hours postinitiation of loading infusion (100 mg/kg in 1 hour). Further significant improvement induced by poloxamer 188 but not placebo was observed ≥ 7 hours postinfusion, resulting in a significant reversal of the microvascular changes to steady-state values.