This is a Phase III multicenter, randomized, double-blind, placebo-controlled study. The purpose of the study is to assess the efficacy of FLOCOR (Poloxamer 188) in the treatment of vaso-occlusive crises in sickle cell disease. Flocor is an agent with rheologic properties that is felt to be capable of decreasing cell-to-cell interactions caused by hydrophobic interactions. The number of patients to be studied has been reduced from the initial target of 350 to 224 patients. To date, 150 patients have been enrolled as a part of a multicenter collaborative trial. An initial meeting of the data and safety monitoring board has reviewed the first 50 patients, and concluded that there was no significant difference in side effects between the placebo and the treatment groups. The blind for the study will be broken at 224 patients, and efficacy determined at that time. If the efficacy as suggested by pilot studies is confirmed, this may become the first widely used agent capable of positively affecting acute vaso-occlusive crisis of sickle cell disease, which would be a landmark in the treatment of this disorder.