Victims of major electrical trauma frequently suffer extensive skeletal muscle and nerve damage, which is postulated to be principally mediated by electroporation and/or thermally driven cell membrane permeabilization. We have investigated the efficacy of two blood-compatible chemical surfactants for sealing electroporated muscle membranes. In studies using cultured skeletal muscle cells, poloxamer 188 (P188; an 8.4-kDa nonionic surfactant) blocks, and neutral dextran (10.1 kDa) substantially retards, carboxyfluorescein release from electropermeabilized cell membranes. To test whether P188 administered intravenously could have the same therapeutic effect in vivo, the rat biceps femoris muscle flap attached by its arteriovenous pedicle was electropermeabilized until its electrical resistivity dropped to 50% of the initial value. P188 (460 mg/kg) administered intravenously 20 min postshock restored the resistivity to 77% of the initial value. When P188 was administered intravenously 5 min before shock, a dose-dependent impedance recovery rate was observed. Neither neutral dextran (460 mg/kg) nor sterile saline was effective. Histopathologic studies indicated that postshock poloxamer administration reduced tissue inflammation and damage in comparison with dextran-treated or control tissues. Electrophysiologic evidence of membrane damage was not observed in flaps of animals pretreated with poloxamer. These results suggest that it may be possible to seal in vivo tissue membranes injured by electrical, thermal, or other membrane-damaging forces.