BACKGROUND: Treatment and disposal of Korean food waste encounter technical difficulties due to a high-salt problem. In order to increase methane production from food waste by using osmoprotectants, which are known to overcome osmotic stresses in many plants and other organisms, osmoprotectants including glycine betaine, choline, carnitine and trehalose were added to salt-containing food wastes for anaerobic digestion. RESULTS: For NaCl-amended food wastes containing 10 and 35 g L-1 NaCl, glycine betaine and choline increased methane production by about twofold compared to food waste without any osmoprotectants. For non-washed food waste containing 11.6 g L-1 NaCl, glycine betaine increased methane production by about sixfold. Among these osmoprotectants, glycine betaine was the most effective for increasing methane productivity in anaerobic digestion of food waste with salinity. Analysis of glycine betaine in cell extracts using high-performance liquid chromatography showed that glycine betaine accumulated in the cells of anaerobic sludge. CONCLUSION: Osmoprotectants significantly enhanced methanization of high-salt food wastes by alleviating the salt-induced physiological stresses in microorganisms. The application of osmoprotectants provided an effective substitute for other conventional methods to reduce inhibitory effects of high salt, such as dilution and co-digestion. (C) 2008 Society of Chemical Industry.