Quantitative structure-toxicity relationships were developed for the prediction of toxicity to Vibrio fischeri using the CODESSA treatment. A four-parameter correlation was found for a class of ionic liquids based on halide. All the descriptors utilized are calculated only from the structures of the molecules, which makes it possible to predict unavailable or unknown ILs, in gas phase and in water (PCM treatment). Satisfactory correlations with the same descriptors were found for both cases but the employment of descriptors calculated in solvent assure a better correlation and a bigger reliability on the foresight. (C) 2011 Elsevier B.V. All rights reserved.