J. Chem. Inf. Model. In Journal of Chemical Information and Modeling, Vol. 52, No. 5. (7 April 2012), pp. 1124-1131, doi:10.1021/ci3000419 We propose a new, robust benchmark, called Percentage Round Tripping of Canonical Isomeric SMILES (%RTCS), for assessing the ability of chemical nomenclature software to convert chemical structures to names and chemical names to structures. The benchmark is based on a string comparison between canonical isomeric SMILES generated from the original structure and the resultant structure from round tripping. Using the latest version of the OpenEye chemical nomenclature toolkit, Lexichem v2.1.0, we report %RTCS values of over 92% on average for a variety of challenging compound collections. Edward Cannon - Egon Willighagen