RheothRx (Glaxo Wellcome Inc, Research Triangle Park, NC; poloxamer 188) Injection is a nonionic surfactant with hemorrheologic properties that suggest it may be useful in treating acute painful episodes (vasoocclusive crises) of sickle cell disease (SCD). We conducted a randomized, double-blind, placebo-controlled pilot study to evaluate the safety and efficacy of poloxamer, formulated as RheothRx Injection, in 50 patients with SCD. Patients with moderate to severe painful episodes requiring parenteral analgesics were randomized to receive a 48-hour infusion of either RheothRx or placebo. Pain was assessed every 4 hours. Efficacy endpoints included: (1) painful episode duration, (2) days of hospitalization, (3) quantity of analgesics used, and (4) pain intensity scores. Three subgroups of patients were considered for efficacy analyses based on the actual duration of the study drug infusion and the completeness of pain score data collection. Compared with placebo and depending on the subgroup, RheothRx-treated patients showed a 16% to 45% decrease in duration of painful episodes, a 1- to 2-day reduction in hospital stay, a threefold to fivefold reduction in analgesic requirements, and a 1-point reduction (using a 5-point scale) in average pain intensity scores at 72 hours. RheothRx was well tolerated; no clinically significant differences were observed between treatments with respect to adverse experiences or other safety measures. In addition, there were no differences between treatment groups in the incidence of recurrent painful episodes. In this study, RheothRx significantly reduced total analgesic use and pain intensity and showed trends to shorter duration of painful episodes and total days of hospitalization. In patients with moderate to severe vasoocclusive pain, RheothRx was safe and may offer a therapeutic benefit.