Highly concentrated melt systems consisting of choline chloride (ChCl) and up to 50 wt% of carbohydrates, corresponding to carbohydrate concentrations of 2.9 to 3.1 mol/L, have been used for the conversion of the carbohydrate content into 5-hydroxymethylfurfural (HMF) in the presence of catalysts. Apart from the monosaccharides d-fructose and d-glucose, the disaccharide sucrose and the polyfructan inulin were successfully converted into HMF. The reported conditions with short reaction times at high concentrations may allow for high space-time yields, which may be of interest for the development of efficient continuous processes for the conversion of carbohydrates into HMF. In a preliminary ecological evaluation, the ChCl/d-fructose system is compared to other representative solvents for the synthesis of 5-hydroxymethylfurfural. The melts have an inherent low toxicological impact due to their negligible vapour pressure. © 2009 The Royal Society of Chemistry.